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There is a growing interest in enhancing the bioactivity of TC4-based metallic biomaterials, which are known for their excellent biocompatibility. Bioactive glass (BG) has been recognized for its high potential in promoting bioactivity, particularly in osteo tissue engineering. This study focuses on investigating the influence of BG addition on the microstructure and electrochemical properties of TC4 coatings. The TC4/BG composite coatings were fabricated through laser cladding, and their microstructure was characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The electrochemical properties of the coatings were assessed through electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests in three different solutions. The results revealed that the incorporation of BG had a significant impact on the microstructure of the TC4 coatings, leading to the formation of a well-defined interface between the TC4 matrix and the BG aggregates. The distribution of BG aggregates within the TC4 matrix coating was found to be random and unrelated to the specific regions of the coating. The metallographic microstructure variations were attributed to different heat dissipation conditions during the laser cladding process. Furthermore, the electrochemical corrosion behavior of TC4/BG composite coatings reveals that they exhibit stability similar to that of passive films and good resistance against media corrosion compared to TC4, while also showing enhanced corrosion resistance in 3.5 wt% NaCl and Dulbecco's modified Eagle medium (DMEM) solutions, indicating their potential for biomedical applications; however, the corrosion resistance decreases gradually in all solutions, potentially due to the elevated Cl− concentration. Further research can explore bioactivity enhancement of TC4/BG composite coatings and investigate the long-term stability and biological response of these coatings in diverse physiological environments. [ABSTRACT FROM AUTHOR]

In order to improve the wear resistance of offshore drilling equipment, CoCrFeNiMn high-entropy alloy coatings were prepared by cold spraying (CS) and high-speed oxygen fuel spraying (HVOF), and the coatings were subjected to vacuum heat treatment at different temperatures (500 °C, 700 °C and 900 °C). The friction and wear experiments of the coatings before and after vacuum heat treatment were carried out in simulated seawater drilling fluid. The results show that CoCrFeNiMn high-entropy alloy coatings prepared by CS and HVOF have dense structure and bond well with the substrate. After vacuum heat treatment, the main peaks of all oriented FCC phases are broadened and the peak strength is obviously enhanced. The two types of coatings achieve maximum hardness after vacuum heat treatment at 500 °C; the Vickers microhardness of CS-500 °C and HVOF-500 °C are 487.6 and 352.4 HV0.1, respectively. The wear rates of the two coatings at room temperature are very close. CS and HVOF coatings both have the lowest wear rate after vacuum heat treatment at 500 °C. The CS-500 °C coating has the lowest wear rate of 0.2152 mm3 m−1 N−1, about 4/5 (0.2651 mm3 m−1 N−1) of the HVOF-500 °C coating. The wear rates and wear amounts of the two coatings heat-treated at 700 °C and 900 °C decrease due to the decrease in microhardness. The wear mechanisms of the coatings before and after vacuum heat treatment are adhesive wear, abrasive wear, fatigue wear and oxidation wear. [ABSTRACT FROM AUTHOR]

A surface functionalization system targeted for iron-based materials is developed by combining two biodegradable components, iron oxide nanostructured arrays and polycaprolactone (PCL) coatings. Iron oxide nanoporous and nanotubular arrays are superior surface functionalization matrices, while their stability and cytocompatibility can be further improved by PCL coatings, the morphology of which can modify the drug release behavior. The biodegradation behavior of this system was investigated firstly by electrochemical tests, and further biodegradation information (including the surface morphology and chemical composition) was collected from samples used in a long-term in vitro cytocompatibility test over 21 days of incubation with human adipose-derived stem cells (ADSCs). Moreover, the drug release behavior of these arrays coated with various PCL coatings was studied using tetracycline as a model drug. Experimental results demonstrate that PCL coatings can endow iron oxide nanostructured arrays a proper biodegradation behavior with bioactive degradation products on the surface, also leading to high cytocompatibility characterized by the production of collagen type I and cell distribution on the PCL-coated samples. Furthermore, with the barrier effect of PCL, the whole functionalization system shows sustainable drug release behavior. Unlabelled Image • Surface functionalization system composed of nanostructured arrays and PCL coatings. • PCL coatings with different morphologies and various roughness are fabricated. • Degradation behavior of this system can be tailored by the morphology of PCL coating. • PCL coatings improve the cytocompatibility of nanostructured arrays significantly. • Drug release behavior can also be modified by PCL coatings with different properties. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a non-toxic Ce-based conversion coating was obtained on the surface of bio-medical AZ31 magnesium alloys. The micro-morphology of the coating prepared with optimal technical parameters and immersed in physiological solution (Hank''s solution) in different time was observed by scanning electron microscopy (SEM), composition of the cerium conversion coating and corrosion products in Hank''s solution were characterized by X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS), respectively. In addition, the corrosion property in Hank''s solution was studied by electrochemical experiment and immersion test. The results show that the dense Ce-based conversion coating is obtained on the surface of AZ31 magnesium alloys in optimal technical parameters and the conversion coating consists of a mass of trivalent and tetravalent cerium oxides. The cerium conversion coating can provide obvious protection of magnesium alloys and can effectively reduce the degradation speed in Hank''s solution. Also the degradation products have little influence on human body. [Copyright &y& Elsevier]

Abstract: In this paper, neodymium-based conversion coating is used as a substitute for toxic chromate conversion coating on AZ91D magnesium alloys. Its formation and growth were observed via SEM, EDS, XPS, electrochemical tests and weighting experiment. The influence of post-treatment on neodymium conversion coating was measured by FTIR and electrochemical experiments in terms of morphology, component, surface functional group and corrosion resistance. The dissolution of matrix and the deposition of neodymium/magnesium oxides compete with each other in initial time. Then the deposition of neodymium oxides dominates the process. Compact coating is obtained after 20min immersion and it is mainly made of neodymium oxides and a small amount of magnesium oxides/hydroxides. The coating post-treated is rich in OH− and PO4 3+. The post-treatment can improve the corrosion resistance of the neodymium conversion coating effectually examined by EIS. [Copyright &y& Elsevier]

NiTi 98-x Si x C 2 (x = 0, 4, 8 wt%) coatings were prepared on Ti-6Al-4V substrate by laser cladding to improve the surface mechanical properties of NiTi coatings. The effects of Si content addition on the microstructure, phase composition, microhardness, and tribological properties of the coatings were systematically analyzed. The results show that NiTi 98-x Si x C 2 (x = 0, 4, 8) coatings are mainly composed of NiTi, NiTi 2 , TiC, and Ti 5 Si 3 phases. The rod-like phase of Ti 5 Si 3 was found in NiTi 90 Si 8 C 2 coating, while the rod-like phases were found broken. The fragmentation of the rod-like phase is related to the growth of the NiTi phase around it. At the same time, TEM results show that the NiTi (B2) phase and Ti 2 Si second phase are exited in the NiTi 90 Si 8 C 2 coating. Ti 2 Si, which has not been decomposed into Ti 5 Si 3 , remains during the laser cladding process. In addition, the eutectic structure in NiTi 90 Si 8 C 2 coating was observed in some regions. The average microhardness of the NiTi 98-x Si x C 2 (x = 0, 4, 8) coating were at 534.08 HV 0.5 , 598.06 HV 0.5 , and 974.08 HV 0.5 , respectively. The wear resistance of NiTi 98-x Si x C 2 (x = 0, 4, 8) coatings increased with the increased Si content. The NiTi 90 Si 8 C 2 coating exhibits the highest microhardness (974.08 HV 0.5) and wear resistance (friction coefficients, wear trace, widths loss weight, and wear rate are 0.320, ~1.25 mm, 12.2 mg, and 5.78 × 10−6 g/Nm, respectively). In NiTi 90 Si 8 C 2 coating, Ti 5 Si 3 phase plays a significant role in the second phase strengthening to improve its tribological properties. The above analysis confirms that NiTi 90 Si 8 C 2 coating has optimal tribological properties. [Display omitted] • NiTi 90 Si 8 C 2 coatings are mainly composed of NiTi, NiTi 2 , Ti 5 Si 3 , and TiC phases. • The fragmentation of Ti 5 Si 3 phase is related to the growth of NiTi phase around it. • Ti 2 Si phase and the eutectic structure were found in NiTi 90 Si 8 C 2 coating. • The microhardness of NiTi 90 Si 8 C 2 coating is 1.8 times than NiTi 98 C 2 coating. [ABSTRACT FROM AUTHOR]

The poor surface properties of Mg Li alloys and the excellent comprehensive performance of high-entropy alloy (HEA) coatings are highly complementary. This study uses laser cladding technology to deposit an AlTiVNiCu/Cu–Al gradient functional coating with favourable wear and corrosion properties on Mg Li alloy substrates. Through the design of the gradient coating structure, laser cladding is used to coat HEA layers on low-melting-point Mg Li alloys, which effectively reduces further dilution of Mg and Li in the substrate. Notably, the Mg content in the prepared AlTiVNiCu protective layer is only 2.34 %. Furthermore, the microstructure, phase structure, microhardness, tribological and corrosion properties of the gradient coating are systematically studied. The protective layer consists of V-rich BCC 1 , (Ni, Ti)-rich BCC 2 , Cu-rich FCC, Mg-rich BCC 3 and nanoscale β -Ti phases, with a predominance of body-centered cubic (BCC) structural phases. The average microhardness is 547.46 HV0.3. Under a load of 3 N, the average friction coefficient of the protective layer is 0.54, with a wear volume of only 2.87 % compared with that of the substrate, which is satisfactory wear resistance. In a 3.5 wt% NaCl solution, the protective layer exhibits the highest corrosion potential (−0.49 V SCE , where SEC denotes saturated calomel electrode), and the lowest corrosion current density (1.14 × 10−6 A·cm−2), representing a remarkable enhancement compared with those of the substrate (−1.57 V SCE and 5.41 × 10−4 A·cm−2). [Display omitted] • Laser-cladded AlTiVNiCu HEA coatings were designed and prepared on Mg Li alloy. • LC-Cu 6 Al layer helps to balance the thermal mismatch between the HEA coating and Mg Li. • HEA coatings consist of V-rich, (Ni, Ti)-rich, Cu-rich, Mg-rich and β-Ti phases. • HEA coatings show good wear resistance with a wear volume of 2.87 % of the substrate. • HEA coatings have higher E corr and lower i corr values for good corrosion resistance. [ABSTRACT FROM AUTHOR]

• A metallurgical AlCuTiVCr HEA coating was prepared on Mg-Li alloy. • Cu-Al layer can balance the thermal matching disparity among HEA layer and Mg-Li. • HEA coating consists of (V, Cr)-rich BCC 1 , Mg-rich BCC 2 , AlCu 2 Ti and β-Ti phases. • The corrosion resistance of Mg-Li alloy was significantly improved. AlCuTiVCr/Cu-Al lightweight high-entropy alloy gradient coating was successfully prepared by laser cladding to improve the corrosion resistance of Mg-Li alloy. The boundaries between AlCuTiVCr protective layer, Cu-Al transition layer and Mg-Li alloy substrate are distinct, forming an excellent metallurgical bonding. The gradient coating design has effectively balanced the thermal matching difference between HEA coating. The prepared AlCuTiVCr protective layer comprises (V, Cr)-rich BCC 1 , Mg-rich BCC 2 , AlCu 2 Ti and β-Ti phases. The Cu-Al transition layer is composed of β-Li, Cu 2 Mg and Al 2 Cu 3 phases. The corrosion potential of AlCuTiVCr protective layer (−0.46 V SEC) is 1.09 V SEC higher than that of Mg-Li alloy (−1.55 V SEC), while the corrosion current density of the protective layer (9.41 × 10−7 A cm−2) is about three orders of magnitude lower than that of the substrate (5.97 × 10−4 A cm−2). [ABSTRACT FROM AUTHOR]

NiTi, NiTi-4Si, and NiTi-4Si-2YF 3 coatings were prepared on Ti-6Al-4V substrate by laser cladding to obtain composite multilayer protective coating for composite structure. The effects of Si and YF 3 addition on the microstructure, phase composition, microhardness, and phase transformation of the coatings were systematically analyzed. The coatings are mainly composed of NiTi, NiTi 2, and TiN phases. The addition of YF 3 results in the decrease of the dendrite TiN phase in the coating. TEM results show that the core-shell structure is observed in NiTi-4Si coating. The β -Ti phase was surrounded by the shell NiTi 2 phase. After the addition of YF 3 , the core-shell structure was found to disappear. With the addition of the Si element, the eutectic structure was found in the coatings. The eutectic structure is mainly composed of NiTi (B2) and Ti 2 Si phases. According to the SEAD result, there are crystallographic orientation relationships (ORs) between NiTi (B2) phase and Ti 2 Si phase as follows: 1 ¯ 11 B 2 / / 1 ¯ 23 Ti 2 Si. The average microhardness of the NiTi, NiTi-4Si and NiTi-4Si-2YF 3 coatings were at 468.33 HV 0.5 , 499.86 HV 0.5 , and 433.65 HV 0.5 , respectively. At the same time, the uniformity of the NiTi phase in NiTi-4Si-2YF 3 coatings is improved, which is conducive to a more complete phase transition. [Display omitted] • With the addition of Si element, the eutectic structure was found in the coatings. • The addition of YF 3 results in the decrease of the dendrite TiN phase in coatings. • the core-shell structure (NiTi 2 @ β -Ti) is observed in NiTi-4Si coating. • The NiTi-4Si-2YF 3 coating exhibits the lowest microhardness. [ABSTRACT FROM AUTHOR]

The new parameter ε we proposed in this study is to be more conducive to the hardness design of high-entropy alloy coatings. Here, the parameter ε is defined as the ratio of the atomic size mismatch to the atomic stacking mismatch. This parameter can be used as the criterion for measuring the magnitude of lattice distortion caused by the atomic size effect, which reveals the influence of the atomic size effect on the hardness of the alloy. We collected nearly 100 groups of on high-entropy alloy coatings in order to verify the feasibility of parameter ε, and to analyze the relevant data from available literatures by using the parameter ε. We found that the hardness value of the high-entropy alloy coatings showed monotonicity with the ε increased. When ε < 6.4, the phase structure of the coating is mainly fcc phase, the increase in hardness of the coating is smaller with the increments of ε. The opposite of bcc phase as the main phase for ε > 6.4, hardness value of the coating escalates with the increase of parameter ε. Based on this finding, it is suggested that the parameter ε can then be used to design a high-entropy alloy coatings with the desired hardness. • The influence of atomic size effect on the hardness of high-entropy alloy coating is briefly analyzed. • A dimensionless parameters is proposed and tested using available experimental data. • The new criterion is able to predict the hardness of high-entropy alloy metallic coatings. [ABSTRACT FROM AUTHOR]