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In this work, the microstructure of titania coating fabricated on the surface of hydrostatically extruded titanium grade 4 with the use of the micro-arc oxidation method was studied. The surface topography and microstructure investigations performed with atomic force microscopy and scanning and transmission electron microscopy revealed that, by using an Na2HPO4 electrolyte, a well-adherent porous coating is produced on the top surface and side walls of the extruded rod. The distribution of chemical elements was analyzed by using energy dispersive X-ray spectroscopy. The chemical elements dissolved in the electrolyte i.e. (Na, P and O) incorporated into the coating. Sodium locates preferentially in the outer part of the coating, while phosphorus and oxygen are distributed throughout the whole coating. The most relevant finding shows that a grain refinement caused by a hydrostatic extrusion provoked an increase in density of high-angle grain boundaries (HAGB), which in turn secured the formation of a continuous amorphous layer close to the substrate. The presence of this layer compensates for the effect of anisotropic substrate, producing a comparable and homogenous microstructure with a large number of micropores.

In this work, a post treatment of laser surface melting (LSM) has been employed on Stellite 6 and 10 wt.% Mo-alloyed Stellite 6 hardfacings deposited by plasma transferred arc (PTA) process. LSM process refined the microstructures of both hardfacings, while favoring a network-like complex carbide dominated microstructure in the Mo-alloyed version. With reference to the PTA Stellite 6 hardfacing, LSM process led to an increment in surface hardness albeit a subsequent reduction of wear loss at room temperature, where abrasive wear mechanism was dominant. At 500 °C, oxidative wear contributed to the progress of wear by favoring CoO and Co3O4 type tribo-oxides on the contact surfaces of the PTA and LSM’ed hardfacings, respectively. However, Co3O4 type tribo-oxides exhibited poor mechanical stability, than CoO, which led to easier removal from the contact surface and aggravated the wear loss by abrasive wear mechanism. In this respect, LSM’ed hardfacings exhibited higher wear loss than PTA Stellite 6 hardfacing at 500 °C, unlike room temperature.

In this study, the effect of Co addition on the microstructure and creep rupture properties of 9Cr-1.8W-xCo weld metals is investigated. Herein, stick electrodes were fabricated for producing weld metals with 0.5, 1.0, and 1.5 wt pct Co and without Co, which were then processed by post-welding heat treatment at 760 °C for 4 hours. The microstructures of weld metals, including the prior austenite grain size, tempered martensite lath size, delta ferrite content, and precipitate quantity and size, were characterized via optical microscopy, scanning and transmission electron microscopy, and electron backscattered diffraction. The precipitates were identified by X-ray diffraction after they were extracted from the matrix. The Curie temperature was determined via differential scanning calorimetry, which allowed the evaluation of diffusion rate as a function of Co content. The weld metals were mechanically characterized by creep rupture tests conducted at 675 °C under 150 MPa and by hardness and tensile tests conducted at room temperature as well as Charpy impact tests conducted at various temperatures from − 40 °C to 60 °C. The results obtained herein suggest that the addition of Co significantly increases the creep rupture time of 9Cr-1.8W steel (by approximately 20 times than that of Co-free steel), reduces the prior austenite grain size and tempered martensite lath size, hinders the formation of detrimental delta ferrite, and promotes the formation of precipitates with slightly larger size. Herein, the highest creep resistance from the viewpoint of creep rupture time was obtained for 9Cr-1.8W weld metal with 1.5 wt pct Co. Furthermore, the results suggest that a finer and more stable substructure is required for improving the creep resistance.

Electron beam surface melting has been applied as a posttreatment to plasma-transferred, arc-deposited Stellite 6 hardfacing and its molybdenum-alloyed version. Molybdenum addition increase...

PurposeThe purpose of this study is to investigate the effect of electron beam surface melting (EBSM) on the properties of Plasma Transfer Arc (PTA) deposited Stellite 12 hardfacing.Design/methodology/approachFor this purpose, structural characterization and dry sliding wear tests have been conducted on the hardfacings at room temperature. The wear tracks formed on the surfaces of the hardfacings were examined by a stylus-type profilometer and a scanning electron microscope.FindingsRefinement of the matrix and the carbides following EBSM process led to about 15 per cent increment in hardness as compared to PTA state. Despite an increase in the surface hardness, EBSM’ed hardfacing exhibited about 50 per cent lower sliding wear resistance than PTA hardfacing against alumina ball. According to the worn surface examinations, reduction in the wear resistance of Stellite 12 after EBSM process has been associated with the extensive refinement of the carbides which made them easier to be removed from the matrix during the sliding contact.Originality/valueThe authors of current study have applied EBSM to PTA deposited Stellite 12 hardfacing alloy to investigate if the surface structure and properties could be improved. More specifically the dry sliding wear performance of PTA and EBSM’ed hardfacings have been focused in the scope of this study. To the best of the authors’ knowledge, this approach, i.e. use of EBSM as a post deposition treatment of Stellite 12 hardfacings, has not been reported in open literature.

In the scope of this study, quenched and tempered H13 steel samples were subjected to conventional (CN) and low temperature (LTN) gas nitriding in a fluidized bed reactor. Structural examinations revealed that surfaces of the CN sample were covered with about 1-2 µm thick compound layer (CL) with an underlying ~30 µm thick nitrogen diffusion zone (NDZ), while outer surface of the LTN sample consisted of ~25 µm thick NDZ. The surface hardness values were measured as 1320 HV0.1for LTN sample and 1220 HV0.1for CN sample. Under impact sliding conditions, wear mechanisms of the CN and LTN samples were determined as “oxidation + fatigue” at RT and “plastic deformation” at 600 °C. As a general trend CN sample exhibited better impact sliding wear resistance compared to LTN sample both at RT and 600 °C.

Aluminum doped zinc oxide (ZnO:Al) thin films via 1.2 at. % Al content was deposited on p-type silicon wafers by using sol-gel dip coating technique to compare the effect of post treatment ambient on electrical characteristics of ZnO:Al/p-Si heterojunction. The annealing environment treatment was performed at 700 °C for 60 min under various gas ambients such as, air, argon, nitrogen, and vacuum. The deposited heterojunction samples were characterised in order to clarified its morphology and crystalline structure. The films showed an orientation along c-axis and the best electrical properties (0.75 × 10 −4 Ω cm) were obtained for the sample prepared in vacum. The changes in electrical properties and current-voltage performance were compared with each other after p-n junction was annealed under different ambient conditions. The heterojunction electrical parameters were determined Therefore, it was possible to make an annealing ambient comparison of the heterojunction for the cost-effect production by using sol-gel dip coating technique to use as the diode in electronic devices.

This work has been initiated with the aim of increasing the success of micro-arc oxidation coatings fabricated on aluminium alloys against degradation under sliding contact conditions at high temperatures. For this purpose, the 7075 Al alloy has been micro-arc oxidised in an aluminate-based electrolyte with or without the adding monoclinic ZrO2 particles. Microstructural analyses revealed that the coating synthesised in a ZrO2-added electrolyte consisted of a ZrO2 particles participated Al2O3-based outer layer and a monolithic Al2O3-based inner layer, which exhibited similar features with that of the synthesised in the ZrO2-free aluminate-based electrolyte. Moreover, the coating fabricated in the ZrO2-added electrolyte exhibited enhanced wear resistance during the dry sliding wear tests conducted at room temperature and had higher durability during the tests done at 300 degrees C. Since the examined coatings were worn by fatigue wear mechanism, their durability during high temperature wear tests was analysed by using the conventional stress-based fatigue approach. From the derived equations, the maximum contact pressures at which coatings can endure 106 contact cycles at 300 degrees C were estimated as 851 and 331 MPa for the coatings fabricated in the ZrO2-added and ZrO2-free aluminate-based electrolytes, respectively.

Tento článek si klade za cíl porozumět mikrostrukturním změnám v Plasma Transfer Arc (PTA) naneseném tvrdokovem z vysokorychlostní oceli (HSS) M2 po zabudování 10% hmotn. Mo legování během nanášení s následným tavením laserového povrchu. Tvrdé povrchové úpravy uložené PTA byly vyrobeny na 4140 oceli. Potom byly Mo legované a nelegované PTA depozity podrobeny procesu laserového povrchového tavení (LSM). U všech výsledných struktur byla provedena komplexní mikrostrukturální charakterizace. Ke zjištění struktury matrice a morfologie karbidů byla použita optická metalografie s použitím vhodných leptacích činidel a SEM mikroskopie ve spojení s technikami XRD. Mikrostruktura PTA byla blízká rovnovážné struktuře M2 HSS obsahující směs feritu / austenitu / martenzitu spolu skarbidy typu MC, M2C a M6C. Zatímco LSM M2 HSS způsobil vyšší podíl martenzitu a jemnějších zrn ve struktuře, což mělo za následek zvýšení tvrdosti. Přidání 10% hmotn. Mo mění karbidy z MC a prutů jako M2C na vláknité M2C a rybí kosti jako M6C. LSM depozit M2 HSS PTA legovaných Mo vedlo k celkovému snížení podílu karbidů M6C a vláknitých karbidů M2C doprovázených poklesem tvrdosti. The article aims to comprehend the microstructural changes, in Plasma Transfer Arc (PTA) deposited M2 high speed steel (HSS) hardfacings upon incorporation of 10wt% Mo alloying during deposition followed by laser surface melting. PTA deposited hardfacings were produced over 4140 steel. Then Mo alloyed and unalloyed PTA deposits were subjected to laser surface melting (LSM) process. A comprehensive microstructural characterization for all the resultant structures was carried out. Optical metallography using appropriate etching reagents and SEM microscopy in conjunction with XRD techniques were employed to ascertain the matrix structure and carbides morphology. The PTA microstructure was close to equilibrium structure of M2 HSS containing mixture of ferrite / austenite / martensite along with MC, M2C and M6C type carbides. While the LSM of M2 HSS caused higher fraction of martensite and finer grains in the structure resulting in increment in hardness. 10-wt% Mo addition changes the carbides from MC and rod like M2C to fibrous M2C and fishbone like M6C carbides. The LSM of Mo alloyed M2 HSS PTA deposits led to an overall decrease in the fraction of M6C carbides and fibrous M2C carbides accompanied by a decrease in hardness.

Plasma electrolytic oxidation (PEO) treatment of Mg alloys improves their wear resistance by increasing their surface hardness, but also leads to high coefficient of friction (COF) values. The sliding counterfaces and the conditions under which PEO-coated Mg alloys operate affect their COFs. PEO-coated AZ31 alloy sliding against hydrogenated DLC (a-C-H) coated steel yields a low COF of 0.13 under the ambient conditions. The current study investigates the effect of the test temperature on the tribological behavior of PEO-coated AZ31 Mg samples sliding against the a-C-H coated counterface at temperatures up to 300 °C. According to the COF vs. wear rate diagram constructed in the temperature range of 25–250 °C, lower COF values and wear rates were exhibited by PEO-coated AZ31 sliding against a-C-H compared to uncoated AZ31 sliding against a-C-H, and PEO coated AZ31 sliding against an uncoated ASTM 52100 steel. The PEO-coated AZ31 produced the lowest COF of 0.03 at 200 °C. The application of PEO to the Mg alloy automotive cylinder bores running against DLC-coated piston rings and/or PEO-coated Mg alloy pistons running against DLC-coated bores could provide a new approach for the prevention of seizure and hot scuffing in lightweight engines in the temperature range between 150–250 °C.

Purpose The purpose of the study is to examine the sliding wear performance of plasma transfer arc (PTA) deposited and laser surface melted (LSM) Mo modified Stellite 12 hardfacings under high contact stresses (i.e. >20 GPa). Design/methodology/approach For this purpose, after structural characterization, sliding wear tests have been conducted using sphero-conical diamond indenter as the counterface with different normal loads. The wear tracks formed on the hardfacings were examined by atomic force microscopy and scanning electron microscopy. Findings Both hardfacings showed severe wear (at high contact stress levels ranging from 24 to 41 GPa), which progressed by plastic deformation, although the wear resistance of LSMed hardfacings was better than the PTA hardfacings by a factor of two due to its near surface microstructure characterized as carbide-rich zone. Originality/value Sliding wear characterization of a promising 10 Wt.% Mo modified version of commercial Stellite 12 hardfacings (as reported previously by authors) was done in as PTA and LSMed states using nanomechanical test system. To the best of authors’ knowledge, no report is available in the open literature on such hardfacings under these testing conditions.

This study investigates the effect of 10 wt% Mo alloying of NiCrBSi hardfacing on the microstructure and dry sliding wear performance at room temperature and elevated temperatures up to 700 °C. Mo additions refined the boride and carbide phases in the microstructure and formed a Mo-rich boro-carbide along with a 20% drop in its hardness. It further improved the wear resistance at all tested temperatures due to the formation of Mo oxides on the worn surfaces.

This study focuses on the surface modification of a medical grade Co-Cr alloy via combining cold spray and thermal oxidation processes. After deposition of a Ti96-Al4 (wt.%) coating, samples were oxidized at 600 degrees C for 60h in air. Oxidation transformed the coating into a dual-layered structure comprising an outer oxide layer (mainly rutile) with a diffusion layer (mainly oxygen enriched titanium and Ti-Al intermetallics) beneath it. Formation of new phases made the diffusion layer brittle and prone to fracture during pull out tests. Scratch and Rockwell-C tests confirmed good adhesion between the oxide and underlying diffusion layers, having average hardness as 1297 HV and 387 HV, respectively. The dual-layer coating exhibited excellent wear performance in a 0.9wt.% NaCl solution against sliding action of alumina ball as compared to Co-Cr substrate, especially at contact pressures

This study focuses on the biological properties of Ti6Al4V after employing micro-arc oxidation in sodium phosphate- and calcium acetate-containing electrolyte with and without addition of silver acetate. After micro-arc oxidation process, structural features of the surfaces were analyzed by using an energy dispersive X-ray spectrometer equipped scanning electron microscope, an X-ray diffractometer and a Fourier transform infrared spectroscope. The micro-arc oxidation process generated multilayer coatings composed of carbonated hydroxyapatite and titanium oxide layers, while addition of 0·001 mol/l silver acetate into the electrolyte caused incorporation of 0·7 wt.% silver into the coating. The antibacterial activity of the coatings was analyzed by using the Streptococcus mutans American Type Culture Collection 25175 strain. The metabolic activity of the multilayers was evaluated in cultures of a human primary osteogenic sarcoma cell line (Saos-2). In short, incorporation of 0·7 wt.% silver in the form of agglomerated particles, mostly around the micropores of the titanium oxide layer, enhanced the antibacterial efficiency of the fabricated coating to some extent without altering the cell proliferation considerably.

Vliv legování (10 wt% Mo) a následného zpracování povrchu (laserové přetavení povrchu) na vlastnosti a chování byl hodnocen u PTA návaru oceli M2. Vlivem legování Mo došlo ke změně charaketru a povahy jak matrice, tak karbidů v povlaku M2. Naopak, laserové zpracování vedlo ke zjemnění struktury a potalčení precipitace karbidických částic. Navzdory zvýšení povrchové trvrdosti vykazoval povlak po laserovém zpracování pokles odolnosti proti opotřebení. Naopak, návar legovaný Mo zlepšil odolnost proti opotřebení, ačkoli jeho tvrdost poklesla. Důvodem byla tvorba oxidického tribofilmu typu Magneli v Mo legované oceli. The influence of alloying (10 wt% Molybdenum) and post deposition treatment (Laser Surface Melting) on the structural characteristics and wear performance of Plasma Transfer Arc deposited M2 hardfacings have been investigated. The nature of matrix and carbides of M2 hardfacing had changed upon Molybdenum addition while the Laser Surface Melting caused structural refinement and a decrease in carbide volume fraction. Despite an increase in hardness, Laser Surface Melting has resulted in reduction in sliding wear resistance against alumina counterface, while the Molybdenum enhanced the wear resistance even with decrease in hardness. This counter intuitive behaviour is attributed to Magnelli oxide containing tribo-oxide layer formation on the worn surface of Molybdenum alloyed hardfacings.

Laser surface melting (LSM) process has been applied on the plasma transferred arc (PTA) deposited Stellite 12 and 10 wt% Mo alloyed Stellite 12 in this study. Following the LSM process, structural and mechanical property comparison of the LSM’ed surfaces has been made. Hardness of the LSM’ed surfaces was measured as 549 HV and 623 HV for the Stellite 12 and Stellite 12 + 10 wt% Mo deposits, respectively. Despite their different hardness and structural features, the LSM’ed surfaces exhibited similar tribological performance at room temperature (RT), where fatigue wear mechanism operates. However, the wear at 500 °C promotes tribo-oxide layer formation whose composition depended on the alloying with Mo. Thus, addition of 10 wt% Mo into Stellite 12 PTA deposit has remarkably enhanced the high temperature wear performance of the LSM’ed surface as a result of participation of complex oxide (CoMoO4) in tribo-oxide layer.

This study has been initiated to form a TiO2 layer having enhanced biological properties on the surface of a CoCr alloy, which is mostly used in manufacturing of orthopaedic implants. As a novel ap...

Aiming at additional improvements in the properties of Stellite 12 PTA hardfacing alloy deposited on 4140 steel substrate, the authors have adopted a dual approach. During PTA deposition Stellite 12 hardfacing powder was alloyed with 10 wt-% Mo, followed by laser surface melting (LSM). Addition of 10 wt-% Mo, led to an increase in the volume fraction of Co and W-rich complex carbides. Later on LSM executed on the PTA led to the development of unique microstructure near the surface, characterised by the segregation of hard Cr-rich carbides. The resultant layers were subjected to mechanical characterisation, at room temperature, e.g. hardness and wear resistance. It was concluded that combining both approaches i.e. addition of Mo during the hardfacing process followed by LSM of deposited layer gave additional improvements in mechanical properties owing to evolution of a unique carbide structure.

In the present study, wear and corrosion resistances of magnesium alloys were analyzed after coated by micro arc oxidation (MAO) process for potential protection of gear component, which is the most wearing part of a conventional bicycle. Two of the most common magnesium alloys (AZ31 and AZ91) were used in the study and they were oxidized in three different electrolytes (aluminate-, silicate-and phosphate-based). Scanning electron microscopy (SEM) was utilized in order to analyze the coating morphology and wear tracks obtained during wear tests. Energy dispersive X-ray spectroscopy (EDS) analyses were implemented to determine the elemental composition of the coatings. Wear and corrosion tests were applied to compare the performances of the coatings. Experimental results showed that wear and corrosion resistances of the samples generally increased after coated by MAO process and the best protection against wear and corrosion related failures, was achieved by utilizing silicate-based electrolyte for MAO process of magnesium alloys under selected process parameters.

Micro-arc oxidation is a simple, single-step surface modification method used to produce coatings on titanium alloys for biomedical applications. The formation and properties of coatings can be widely controlled by adjusting process parameters such as applied voltage, frequency, processing time and electrolyte composition. In the present study, three different electrolytes were used to obtain well adherent, rough, porous, hydroxyapatite containing, oxide coating on Ti6Al7Nb alloy. Coatings were investigated in terms of their microstructure, chemical composition, roughness, hardness, adhesion strength and biocompatibility. Among the coatings produced in different electrolytes, one of them exhibited both good mechanical properties and bioactivity, while containing crystalline hydroxyapatite on the surface, whereas the other two coatings were mostly amorphous. Thereby, we have proposed an efficient electrolyte containing calcium and phosphorous species in order to modify titanium based alloys to improve their biocompatibility and osseointegration. Such properties are achieved by formation of a rough outer layer with open pores, providing high surface area for cells to adhere, proliferate and migrate into the coating, promoting firm anchorage of the coated implant in the bone.

This study compares the tribological behaviour, of cold sprayed (CS’ed), SiC particle (SiCp) reinforced Al-12Si matrix composite coatings deposited on 1050 grade aluminium, in two different testing environments (dry and water). The increase in hardness with incorporation of SiCp caused the coatings to exhibit lower wear rate and friction coefficient in both testing environments. As an indication of water lubricity, sliding in water imposed superior tribological performance (i.e. lower wear rate and lower friction coefficient) as compared to the dry sliding condition especially at lower wear testing load. In summary, finding of this study revealed that, water could be a promising lubricant for metallic engineering components after coating with SiCp reinforced Al-12Si matrix composites by CS process.

Stellite 12 hardfacing alloy deposited by plasma transferred arc (PTA) process on the 4140 steel substrate was subjected to laser surface melting (LSM) process. The effect of LSM on the PTA deposit was studied in terms of changes in microstructure and resultant variations in sliding wear properties. In the PTA state the microstructure, which consisted of Cr-rich (Cr7C3 and/or Cr23C6) and complex ((CoCrW)6C) carbides in Co matrix, was altered upon the application of LSM process. In short, LSM process led to the formation of a duplex layer, on the surface, consisting of carbide deficient and rich zones whose thickness tended to decrease with increase in the laser scan speed. As the result of formation of carbide rich zone at the outermost surface, LSM process provided an enhancement in surface hardness. On the other hand, the positive effect of LSM process on wear resistance became more apparent at high wear testing load causing carbide cracking and removal on the contact surface of Stellite 12 PTA hardfacing deposit.

In this study, structural characteristics and tribological performance of the coatings deposited on a 1050 quality aluminium substrate by cold spraying of the feedstock consisting of 100% Al–12Si and 25 vol.% SiC + 75 vol.% Al–12Si powders were examined. Wear tests were conducted in air and in water against alumina ball under loads of 1 and 5 N by a reciprocating wear tester at room temperature. Presence of SiC particles in the structure enhanced the wear resistance of the Al–12Si coating both in air and water. As compared to the air testing condition, water containing media provided better tribological performance especially at the wear test load of 1 N. The findings of this study revealed potentiality of water to be used as a lubricant for SiC-reinforced Al–12Si matrix cold spray composite coatings at relatively low wear test loads.

Multi-layer coatings (composed of outer hydroxyapatite and inner titania layers) have been synthesized on Ti6Al4V alloy for biomedical applications by employing micro-arc oxidation at positive and negative voltages of 400 and 80, respectively. Addition of silver nitrate (at concentrations of 0.1 g/L and 0.4 g/L) into the calcium acetate hydrate and disodium hydrogen phosphate anhydrous containing base electrolyte provided an enhancement in bio- and antibacterial activities of the synthesized coating, while imposing precipitation of silver nanoparticles on the hydroxyapatite layer. It is finally concluded that addition of 0.1 g/L AgNO 3 into the base electrolyte is promising for MAO process of titanium-based implants, when the structural characteristics and risk of cytotoxicity are of concern for the synthesized multi-layer coatings.

In the present work, the influence of alumina (Al2O3) and zirconia (ZrO2) incorporation on the structural properties and wear resistance of titania (TiO2) based micro-arc oxidation (MAO) coatings fabricated on Ti6Al4V alloy was studied. For this purpose MAO was employed in a silicate-based electrolyte with and without additions of Al2O3 and ZrO2 particles. The structural properties were determined via X-ray diffraction (XRD) and X-ray photoelectron (XPS) spectroscopy analysis and an energy dispersive spectrometer (EDS) equipped scanning electron microscope (SEM). Furthermore, thermochemical simulations were made by using FactSage 7.3. Mechanical properties of the MAO coatings were determined by hardness measurements and dry sliding reciprocating wear tests. Structural examinations revealed that the MAO coatings fabricated in Al2O3 and ZrO2 added electrolytes comprised of these oxides and their complex forms (Al2TiO5 and ZrTiO4, respectively) along with TiO2 and amorphous silica (SiO2). Although incorporations of Al2O3 and ZrO2 did not remarkably improve the hardness of the MAO coatings, the highest wear resistance was obtained from the one formed in the ZrO2 added electrolyte. On the other hand, the MAO coating fabricated in the Al2O3 added electrolyte exhibited lower wear resistance than that of fabricated in the particle-free silicate-based electrolyte.

This study aims to understand the oxide scale formation on the surfaces of commercial and Mo (10wt.%)-modified Stellite 12 hardfacings deposited on 4140 steel. For this purpose, samples of the hardfacings were isothermally oxidized in air at various temperatures in between 500 and 900 degrees C for 30 h. As a result of changes in the microstructure upon Mo addition, about 50% higher mass gain at all oxidation temperatures was observed. The characteristics of the developed oxide scales were examined by utilizing Raman spectroscopy, scanning electron microscopy and x-ray diffraction analysis. The oxide scale formed over Stellite 12 consisted of CoO-, Co3O4- and Cr2O3-type oxides, while additionally CoMoO4-type complex oxide was detected on Mo-modified hardfacing, more likely at the alloy-scale interface. On the basis of findings of isothermal oxidation tests, the formation mechanisms of this complex oxide imposing better wear resistance as reported in our previous studies were explained during high-temperature wear testing, i.e., dynamic oxidation conditions.

This study was initiated with the aim of extending the usage of magnesium alloys especially in corrosion and wear related engineering applications by coating their surfaces via micro arc oxidation (MAO). Considering the individual influence of phosphate-based and aluminate-based electrolytes on the corrosion and wear performances of the synthesized MAO coatings, respectively, AZ91 magnesium alloy has been subjected to MAO in aluminate-based reference electrolyte with and without additions of Na3PO4 at concentrations of 5 and 10 g/l. As opposed to dry sliding conditions, MAO coatings synthesized in the aluminate-based reference electrolyte did not provide good protection of AZ91 magnesium alloy against wear in corrosive media (0.9 wt% NaCl solution). This study revealed that, addition of 5 g/l Na3PO4 into this reference electrolyte was sufficient for enhanced resistance of MAO coating against chemical and mechanical degradations (i.e. corrosion-wear) without altering its features in terms of surface roughness and thickness.

This study reports on the consolidation of niobium boride powders by cold pressing/pressureless sintering (PS, with or without Co addition) and spark plasma sintering (SPS) techniques. Niobium boride powders (containing NbB, Nb3B4 and NbB2 phases) which were mechanochemically synthesized from Nb2O5, B2O3 and Mg blends and purified by HCl leaching were used as precursor material. The effects of different sintering techniques on the consolidation behaviour, microstructure, densification rate and mechanical properties (microhardness, wear characteristics, elastic modulus, indentation response and fracture toughness) of the bulk products were investigated. PS with Co addition resulted in superior properties than those yielded after PS without Co addition and SPS. Bulk niobium boride products having relative density of 93-98%, microhardness of 24-28 GPa, wear volume loss of 2.8-4.5 x 10(-4) mm(3), elastic modulus of 508-552 GPa and fracture toughness of 4.05-4.74 MPa m(1/2) were obtained by Co (2 or 5 wt.%) activated PS at 1500 degrees C., Scientific and Technological Research Council of Turkey (TÜBİTAK)

This work provides an overview of organosilane metal pretreatments with a focus on water-based systems. Furthermore, this work aims to point out the key notes for organosilane technology to be fully transferred to industry.

The structure of titanium alloy Ti6Al7Nb (the surface nitride layer, the intermediate layer and the diffusion layer) is studied after nitriding at 950, 1120 and 1250°C for 12 h at atmospheric nitrogen pressure. The thickness of the nitride and diffusion layers is shown to increase with increase in the nitriding temperature. The growth of the nitride layer is accompanied by segregation of aluminum in the intermediate layer.

Purpose This paper aims to study microstructure and high temperature tribological performance of hypo-eutectic CoCrWC hardfacing alloy (Stellite 12) deposited on steel substrate by plasma-transferred arc (PTA) welding technique. Design/methodology/approach Microstructural characterization of the deposited coating was made using electron probe microanalysis, X-ray diffraction and microhardness tester. Dry sliding wear tests were carried out with a ball-on-disc type tribometer at room and elevated temperature. Worn surfaces of the samples were examined by the EDX equipped SEM and Raman spectroscopy. Findings Results revealed that at room temperature and 300°C plasticity dominated wear mechanism was operative. Under oxidation dominated wear conditions (400, 500, 600 and 700°C), testing temperature plays a crucial role on the characteristics of the oxide tribolayers formed on worn surfaces. Development of Cr2O3 in the tribolayer at 600 and 700°C was beneficial in increasing wear resistance of examined coating. Originality/value While the sliding wear performance of Stellite alloys at room temperature has been investigated in details, published studies on tribological behavior of Stellite alloys with varying temperature are scarce. Therefore, the present work was undertaken to study the wear mechanisms and the type of tribolayers formed during sliding wear of PTA welding deposited hypo-eutectic Stellite 12 coating with increasing temperature up to 700°C.

Structural and mechanical properties of La 2 O 3 added (up to 5 wt%) t-ZrO 2 compacts were examined with the aim of optimizing hardness and fracture toughness for room temperature applications. Structural examinations were performed using an X-ray diffractometer and a scanning electron microscope. Mechanical properties of the compacts were determined as modulus of elasticity, hardness and fracture toughness by conducting Vickers indentation tests under test loads of 0.5, 1 and 10 kg. Addition of 0.5 wt% La 2 O 3 deteriorated the room temperature stability of t-ZrO 2 by forming m-ZrO 2 and coarse polygonal grains in the matrix. Higher concentrations (2 and 5 wt% La 2 O 3 ) caused precipitation of La 2 Zr 2 O 7 at the grain boundaries, which also accompanied by a reduction in hardness. Fracture toughness increased with increasing La 2 O 3 content of the compact. Finally, an optimum combination between hardness and fracture toughness was obtained for the 0.5 wt% La 2 O 3 containing compact.

The investigation is focused on the wear behaviour at elevated test temperature of composite Ni–P/SiC deposit, with varying concentration of the reinforcing SiC particles. The phase evolution measured by X-ray diffraction suggests slight crystallisation during wear testing at 200 °C. In coating without reinforcing particles, adhesive wear is accompanied by microcracks. The thermal heat generated and the cyclic loading could have induced sub-surface microcracks. Owing to the effective matrix-ceramics system in composite coatings, fine grooves, abrasive polishing and uniform wearing are observed. Reinforcing particles in the matrix hinder microcrack formation and significantly reduce the wear rate. Triboxidation is confirmed from energy dispersive X-ray spectrometry.

New results about the scratch practical adhesion-resistance of the CoB–Co2B/substrate system developed at the surface of CoCrMo (ASTM-F75) alloy were estimated. The boron diffusion on the surface of the cobalt alloy was conducted using the powder-pack boriding process at temperatures of 1223 and 1273 K with different exposure times for each temperature. The scratch tests over the surface of cobalt borided alloy were performed with a 200 micrometres Rockwell C diamond indenter considering a continuously increasing normal force for the entire set of experimental conditions of the boriding process. The worn tracks produced on the coating/substrate system were analysed by optical and scanning electron microscopy to estimate and identify the critical loads and failure mechanisms, respectively. The results indicated that the critical loads varied between 95 and 142 N as a function of the boride coating thicknesses with a development of various types of failure mechanisms over the surface of the coating/substrat...

The present work studies microstructure and wear resistance of Stellite 12 alloy coating deposited on quenched and tempered AISI 4140 steel substrate using plasma transferred arc (PTA) hardfacing method. The X-ray diffraction, scanning electron microscopy (SEM) micrographs and energy-dispersive X-ray (EDX) analysis indicated that Stellite12 mainly consists of solid solution phase (α-Co, e-Co), chromium-rich carbides (Cr7C3, Cr23C6) and tungsten-containing compounds. The wear properties of PTA hardfaced stellite12 comparing with AISI 4140 steel at room temperature (RT) were investigated by using the ball-on-disc type tribotester. It has been found that the Stellite12 hardfacing coating exhibits superior wear resistance than substrate during dry sliding wear test at RT.

This work examines the role of counterface materials on the tribological behaviour of Mg alloys subjected to plasma electrolytic oxidation (PEO) process and focuses on reducing the sliding coefficient of friction (COF) values of PEO treated surfaces. Surfaces of AZ31 grade Mg alloy were subjected to a PEO treatment in a sodium metasilicate and potassium hydroxide containing electrolyte. Unlubricated sliding wear tests were conducted using counterfaces made of nitride based (N-based), TiN, TiCN, CrN and hydrogenated diamond-like carbon (H-DLC) coated as well as uncoated SAE 52100 grade bearing steel balls. MgO based coatings formed on the surfaces of samples during PEO process increased the wear resistance of AZ31, regardless of the type of counterface material used. Sliding the PEO treated surfaces against counterfaces made of uncoated steel and N-based coatings yielded high COF values of 0.6–0.8 that exceeded those of the uncoated AZ31 against the same counterfaces. During dry sliding of H-DLC counterface on the MgO coating, smooth and stable friction curves with a low steady state COF value of 0.13, were recorded. Therefore, a major drawback of PEO treatment that gives rise to surfaces with high COF could be addressed by running them against H-DLC coated counterfaces, a method that could be applied to development lightweight tribological components that are both sliding wear resistant and have low COF.

Room temperature tribological behavior of the thermally oxidized (at 600 °C for 60 h in air) low-pressure cold spray coatings fabricated on a Co-Cr alloy by deposition of Ti (85–95 wt.%) and Al (5 wt.%) powder mixture with and without the addition of Zn powder (up to 10 wt.%) were examined. At the outermost surface, the thermal oxidation caused mainly formation of a wear resistant TiO2 layer; also containing ZnO over the Zn accumulated regions of the coatings. The presence of ZnO induced a reduction in the coefficient of friction to a value as low as 0.12 against the sliding contact of the Al2O3 counterface for the coating fabricated by deposition of the 5wt.%Zn containing powder mixture.

This study has been carried out to optimise the silver (Ag) content of the coating synthesised on commercially pure titanium (Cp-Ti, Grade 4) for biomedical applications by micro-arc oxidation (MAO) process. The MAO process has been conducted in electrolytes containing silver acetate (AgC2H3O2) at different concentrations between 0 and 0.002 mol L-1. When compared to the base electrolyte, coatings synthesised in >= 0.001 mol L-1 AgC2H3O2 added electrolytes exhibited an antibacterial efficiency of 99.8% against Staphylococcus aureus (S. aureus). Detailed examination revealed that the presence of 0.01 mol L-1 AgC2H3O2 in the electrolyte resulted in incorporation of 1.4 wt-% Ag into fabricated coating consisting mainly of outer hydroxyapatite (HA) and inner titanium oxide (TiO2) layers. In comparison to the Ag-free coating, 1.4 wt-% Ag in the coating lowered the proliferation of SAOS-2 cells, which still tended to grow at a relatively low rate with increasing culturing time.

The structural features, biocompatibility, and mechanical performance of a titania (TiO2) layer with incorporated zirconia (ZrO2) formed by microarc oxidation on commercially pure titanium have been examined in the present study. In comparison to the ZrO2-free TiO2 layer, the ZrO2-incorporated oxide layer was dense and contained ZrTiO4 as a new oxide as well as ZrO2 particles. Associated changes in the microstructure enhanced the mechanical durability of TiO2 layer. Owing to the incorporation of identical biocompatible compounds and almost similar surface roughness, no remarkable difference in bioactivities of the ZrO2-free and ZrO2-incorporated oxide layers was detected after simulated body fluid tests. Copyright © 2015 John Wiley & Sons, Ltd.