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Intermediate α″ phase was constructed in as-printed Ti alloys by introducing interstitial carbon atoms to mitigate the detrimental effects of α′ martensite on ductility. The interstitials served as a lattice modulation limiter to achieve an incomplete atomic shuffle during martensitic transformation process to form metastable α″ phase, followed by stabilizing the α″ to inhibit the growth of α′ martensite. The resulting microstructure, characterized by a dominant α/α′ matrix decorated with fine α″ phase, enhanced twinning formation ability and induced dynamic Hall–Petch and grain refinement strengthening effects. This resulted in simultaneous improvements in both strength and ductility.

FeCoNiSi–Cu, FeCoNiSi–Mn, and FeCoNiSi–Ti equiatomic high entropy alloys (HEAs) were designed and produced via powder technology using spark plasma sintering (SPS). Metallurgical analysis tools, including SEM, XRD, EBSD, were used to investigate the crystal structure and the distribution of the formed phases for the prepared HEAs. The formation of a ductile FCC phase for all the prepared HEAs was observed, while the brittle BCC phase was formed only for FeCoNiSi–Mn HEA. By comparing the results with thermodynamic parameters, it is found that there is a strong agreement for the results with the valence electron concentration rule. FeCoNiSi–Cu and FeCoNiSi–Mn HEAs show 100% relative density, whereas FeCoNiSi–Ti HEA shows only 95%. All the prepared HEAs with Cu, Mn, and Ti additions show high hardness values of 507, 710, and 495 Hv, respectively. Both FeCoNiSi–Cu and FeCoNiSi–Mn HEAs have high compressive strength and yielding strength of 1854 MPa,1390 MPa for FeCoNiSi–Cu HEA and 1565 MPa, 1482 MPa) for FeCoNiSi–Mn HEA, respectively. Although having finer grains, FeCoNiSi–Ti HEA shows the lowest compressive strength and yield strength values. This is due to the tendency of the alloy to form intermetallic compounds and the presence of pores that act as nuclei for crack initiation and propagation. In addition, due to the presence of non-ferromagnetic elements in equiatomic ratio with other ferromagnetic elements (FeCoNi), FeCoNiSi–Cu HEA shows only 59.4 emu/gm for magnetization saturation, but the magnetic properties for both FeCoNiSi–Mn and FeCoNiSi–Ti HEAs nearly disappeared.The electrical resistivity for all the prepared HEAs is very high.

It has been a common method to improve the mechanical properties of metals by manipulating their microstructures via static recrystallization, i.e., through heat treatment. Therefore, the knowledge of recrystallization and grain growth is critical to the success of the technique. In the present work, by using in-situ high temperature EBSD, the mechanisms that control recrystallization and grain growth of an extruded pure Mg were studied. The experimental results revealed that the grains of priority for dynamic recrystallization exhibit fading competitiveness under static recrystallization. It is also found that grain boundary movement or grain growth is likely to show an inverse energy gradient effect, i.e., low energy grains tend to swallow or grow into high energy grains, and grain boundaries of close to 30° exhibit superior growth advantage to others. Another finding is that {10–12} tensile twin boundaries are sites of hardly observed for recrystallization, and are finally swallowed by adjacent recrystallized grains. The above findings may give comprehensive insights of static recrystallization and grain growth of Mg, and may guide the design of advanced materials processing in microstructural engineering.

The lattice square degree, denoted by the c/a value, is a crucial factor that influences the slip mode of α-Ti alloys and thereby affects their plasticity. However, the relationship between the c/a value and the plasticity of α-Ti alloys has not been fully clarified. In this study, the powder metallurgy method (PM) was used to prepare Ti alloys with different square degrees by introducing interstitial O and substitutional Si solutes into α-Ti crystal. Then the mechanical properties, particularly plasticity, and lattice parameters of the resulted alloys were measured. By combining first-principles calculation with experimental studying, a plastic criterion based on the square degree was established. Subsequently, the mechanism of strength and plasticity was investigated by means of the density of states and charge density difference. Finally, the composition of α-Ti alloys with both O and Si solution atoms was designed, whose c/a values were calculated by the first-principles calculation and accorded with the proposed square degree criterion, and then the reliability of this criterion was verified by the experimental results. As a result, a high strength and plasticity α-Ti alloy with tensile strength 1106 MPa and elongation 23.2 % was successfully prepared. The findings of this research offer new insights into the alloying design of α-Ti alloys with high strength and moderate plasticity.

Al-matrix composites, reinforced with two different types of glassy particles and prepared by mechanical alloying, were consolidated via Spark Plasma Sintering (SPS) and hot extrusion to produce high-strength Al–5%Al65Cu20Ti15 and Al–5%Al84Ni7Co3Nb6 composites, along with pure Al sample for comparison. TEM observation and XRD analysis were used to investigate the crystal structure of the prepared powders. Metallurgical analysis tools, including SEM, TEM, XRD and EBSD, were used to investigate the effect of consolidation temperature and processing on the amorphous phase and the distribution of reinforcing particles in the composite. Also, the effect of the consolidation process on the grain morphology and size of the prepared composite was studied. Al-5% Al65Cu20Ti15 was fully densified, compared to nearly 98 % relative density for Al-5% Al84Ni7Co3Nb6 and pure Al sample prepared by hot extrusion. Moreover, Al-5% Al65Cu20Ti15 composite showed the highest hardness and ultimate tensile strength values, which are 63Hv and 226 MPa, respectively. An acceptable elongation of 15 % was also achieved. After SPS, hot extrusion process improved the strength of the composite compared with previously reported Al composites containing higher percents of Al-based glassy articles manufactured using various processing techniques. Homogenous reinforcement distribution, grain refinement and improved wettability between matrix and reinforcement are the key factors on improving the strength of Al–5%Al65Cu20Ti15 composite. The coefficient of thermal expansion (CTE) decreased by adding glassy particles to the Al-matrix, while Al-5% Al65Cu20Ti15 had the lowest values.

ABSTRACTSelective laser melted (SLMed) AlSi10Mg alloys usually fail before necking during tensile tests, which results in inadequate ductility. To overcome this problem, here we introduced Al4C3 nanorods into the primary Al cells of SLMed AlSi10Mg via in-situ chemical reaction. Tensile tests revealed that those in-cell Al4C3 nanorods not only increased the strain-hardening ability of SLMed AlSi10Mg but also delayed the fracture beyond necking. Consequently, 15% of tensile strength increase and 78% of ductility increase were achieved simultaneously. Post-tensile TEM analysis revealed that those in-cell Al4C3 nanorods pinned and accumulated dislocations within cells and thus alleviated stress concentration along cell boundaries.

Laser powder bed fused (LPBFed) AlSi10Mg is recognised for its superior mechanical properties. However, its thermal stability has never been justified. Herein, we exposed as-built AlSi10Mg to different temperatures (200–500°C) for only 3 min to evaluate its thermal stability. Results showed that LPBFed AlSi10Mg had relatively low thermal stability. Only 3 min of thermal exposure at 200°C would deteriorate its tensile strength dramatically. Microstructural analysis revealed that with increasing thermal input, as-built AlSi10Mg exhibited a microstructural evolution similar to annealing of cold-worked metals, namely recovery, recrystallisation followed by grain-growth. The excessive energy stored in as-built microstructure due to fast cooling during LPBF was deduced as the driving force for this phenomenon. Therefore, such microstructural change was at the expense of dislocations stored in the as-built material, which in turn caused deterioration in tensile strength. The present findings may provide guidance for the application of LPBFed AlSi10Mg.

There is a concern regarding sub-surface pores within laser powder bed fusion of Ti-6Al-4V, which can initiate cracks and reduce mechanical properties, especially after machining for surface finishing. This study investigated the effect of laser scanning speed and fine shot peening on the pore characteristics, hardness, and residual stress of Ti-6Al-4V fabricated by laser powder bed fusion using scanning electron microscopy, X-ray micro-computed tomography, Vickers hardness, and X-ray diffraction. As the laser scanning speed increased, the number of pores and pore size increased, which reduced the hardness of Ti-6Al-4V. Most pores were less than 20 µm in size and randomly distributed. The fine shot peening generated plastic deformation and compressive residual stress on the surface, leading to higher hardness, with similar surface properties at all scanning speeds. The depth of compressive residual stress by fine shot peening varied corresponding to the scanning speeds. Increasing the scanning speed accelerated the rate of conversion between the compressive and tensile residual stresses, and decreased the depth of the maximum hardness by the fine shot peening from initial tensile residual stress within Ti-6Al-4V fabricated by laser powder bed fusion, thus reducing the enhancement achieved by the fine shot peening.

Cu matrix composites reinforced by ex-situ added CrB2 ceramic particles were prepared by powder metallurgy and hot extrusion, and then the effect of CrB2 content on microstructure and mechanical properties was studied. Results show that the strength of Cu matrix composites depends mainly on the dispersion degree of CrB2 particles, which is closely corresponded to the content of CrB2 particles. When the content is below 3vol.%, CrB2 particles disperses uniformly in the Cu matrix, and the strength of Cu matrix composites increases continuously with the content of CrB2. However, when the content is above 3vol.%, the strength of Cu matrix composites decreases significantly with the increase of CrB2 content, which is ascribed to the serious agglomeration phenomenon. Although both the electrical conductivity and plasticity decrease with the increase of CrB2 content, they remain quite a high level. The excellent combination properties are obtained when the content of CrB2 is 3vol.%, viz. The tensile strength is 304 MPa, the elongation is 22% and the electrical conductivity is 90 %IACS, better than most of the reported Cu matrix composites especially electrical conductivity prepared by in-situ method. Furthermore, dislocation strengthening caused by thermal mismatch and Orowan strengthen of CrB2 is demonstrated as the main strengthening mechanism of Cu/CrB2 composites, based on the theoretical and experimental investigations.

Oxygen has been known as an effective strengthening element in titanium (Ti) and its alloys. However, an over-dose of oxygen can also lead to embrittlement of Ti alloys. To precisely control and push the limit of oxygen in Ti and its alloys, we studied the decomposition process of Ti oxides in pure α-Ti matrix using an in-situ high-temperature scanning electron microscope. The experimental results revealed that TiO particles decomposed in α-Ti at elevated temperatures and the oxygen atoms gradually diffused into the matrix, following the Fick’s second law. Then, the samples with different oxygen contents were produced using the aforementioned strategy, for which the oxygen content, microstructure, and mechanical properties were measured. The results revealed that the oxygen content can be precisely controlled, which can achieve an ultra-high tensile strength of close to 1100 MPa, at no expense of elongation-to-failure, with incorporating 0.87 wt% oxygen. An analysis showed that the strength contribution from oxygen follows the Labusch law. These findings offer a novel approach to design high-performance Ti alloys with non-toxic and cheap elements.

To investigate the microstructure and mechanical properties of the dissimilar joint between high entropy alloys (HEAs) and Al alloy, FeCoCrNiMn was joined to 6061 Al alloy by friction stir lap welding (FSLW) at tool rotation speeds from 900 rpm to 1800 rpm. Systematic tilting high-resolution transmission electron microscopy patterns were applied to study the interfacial microstructure. A nanoscale (< 250 nm) interfacial layer was found at the 6061/FeCoCrNiMn interface and the phase formed in this layer was identified as Al13Fe4-type intermetallic compound (IMC) with the Fe-sites occupied by HEA elements. Microsegregation of HEA elements was observed in this Al13Fe4-type IMC in two different modes: 1) co-segregation of Cr and Mn and co-depletion of Co and Ni, for the majority of the interfacial layer, and 2) co-segregation of Co and Ni and co-depletion of Cr and Mn, mainly in regions adjacent to the Al alloy side and sporadic in the middle. The maximum tensile lap shear strength reached 151 MPa, which was approximately 73 % of the shear strength of 6061 base material. The joint fracture occurred within Al alloy nearby the interface rather than right along the interfacial layer, suggesting high interfacial metallurgical bonding achieved in this study.

This study aims to improve the mechanical properties of a Ti–2Fe base alloy by adding W solute and performing hot extrusion at a high temperature (1000 °C). W was added at 0, 1, 2, and 3 wt% using the powder metallurgy route and homogenization heat treatment. The as-extruded materials predominantly consisted of α phase with different microstructure morphologies; Ti–2Fe and Ti–2Fe–1W contained equiaxed α grains, while Ti–2Fe–2W and Ti–2Fe–3W showed equiaxed + acicular and acicular shape, respectively. Effective grain refinement was obtained in Ti–2Fe–2W (average grain size: ~1.64 μm), which greatly contributed to the strengthening. The solid solution of W was studied with X-ray powder diffraction, where a proportional increment of β lattice constant occurred as the W solute increased in the matrix (Ti–Fe). Additionally, electron backscatter diffraction analysis revealed that the W solution reduced the intensity of the prismatic texture along the extrusion direction. Based on the experimental evaluations, extruded Ti–2Fe–2W alloy exhibited a maximum yield strength of 925 MPa with excellent elongation 30% at room temperature, indicating a remarkable trade-off in strength and ductility.

Considering the high strength of titanium matrix composites (TMCs) at room and elevated temperatures, the aim of this study was to develop novel TMC Ti-4Fe-3W/2TiC (wt%) utilizing powder metallurgy and subsequent extrusion at different temperatures: the two-phase (α+β) and pure β phase regions. The TiC particle dispersion was almost identical in both composites with variation in the size distribution. However, there was a significant difference in the morphology of the α phase in the matrix. The α+β-extruded composite exhibited globular αp (grain size: 0.7 μm); in contrast, the β-extruded phase showed acicular αs (grain size: 1.5 μm). Additionally, α-Ti was the predominant phase in contact with TiC particles due to the semi-coherent relationship between these two phases. A remarkably high yield strength (1215 MPa) was achieved at room temperature in the α+β -extruded composite, while the β-extruded composite exhibited consistently improved strength at high temperatures. Morphological characterization using atomic force microscopy (AFM) revealed the β phase was slightly harder than the α phase, probably due to the solid solution of Fe and W that predominant in the β phase.

An interesting phenomenon that yielding was observed in the Ti matrix composites with above 4.10vol%TiCp. To clarify the underlying nature, in-situ tensile test was performed, and results indicated that this was caused by cracking at the interface between the aggregated TiCp and Ti matrix, which is quite different from the well-accepted viewpoint. Furthermore, fracture of stronger TiCp prior to weaker TiBw was also found during in-situ tensile test, and a fracture criterion was proposed from the viewpoint of load transfer.

Double shot peening is the development of shot peening by shooting large media as a first shot and re-shooting again with smaller media as a second shot in order to achieve high residual compressive stress and hardness at the surface, while the in-depth effect can still be maintained. This research aims to examine the effect of media type and media size when used in the second shot of double shot peening on hardness, roughness, and residual stress to identify the suitable conditions and compare them with single shot peening, such as conventional shot peening and fine shot peening, which was used as the first shot and second shot. Ti–6Al–4V was used as the substrate material, while various diameter sizes of silica and SUS304 media were selected as the media for the second shot in the process. The results showed that in the case of the larger size of silica media in the second shot of double shot peening, the hardness and residual compressive stress on the surface clearly increased more than with the smaller media due to the higher Almen intensity, which affected impact energy. On the other hand, when shooting with SUS304 media as a second shot, the increment of residual compressive stress and hardness, including roughness reduction on the surface, showed less effect than was the case for silica media, due to the lower Almen intensity, which affected the impact energy transfer. This research found that the condition of shooting with 80 μm of silica media as the second shot could generate the highest hardness and residual compressive stress on the surface, which increased by 14% and 53%, respectively, while roughness was decreased by 20% when compared with single shot peening.

The wide applicability of titanium (Ti) has prompted the analysis to improve its mechanical strength through the addition of different alloying elements. Among these, Ti materials with pre-mixed pure Ti and titanium nitride (TiN) powders as the starting materials have exhibited improved mechanical properties and tribological performance. In this study, the tribological properties of Ti matrix composites with ring-shaped TiN dispersoids were evaluated. The materials were fabricated from pre-mixed pure Ti powder and core–shell structured Ti–(N) powder, which were prepared by heat treatment at 1273 K under N2 gas. The tribological behavior of the Ti–TiN composites was studied by varying the applied load using a ball-on-disk wear test under oil lubrication conditions. The initial familiarity period of the Ti–TiN composites decreased. Subsequently, compared to the pure Ti specimen employed as a reference material, the friction coefficient was significantly lower and more stable. This is attributed to the ring-shaped, hard TiN dispersoids, which prevented the adhesion phenomenon and improved the oil film formability owing to the increase in microhardness and abrasive wear resistance of the nitrogen solid solution in the core region.

For better clarifying the influence of processing factors on the forming quality of the direct powder rolling (DPR) process, finite element simulation based on the modified Drucker–Prager/Cap (DPC) model was established and the key physical parameters of the powder were confirmed by experimental measurements. Subsequently, the effect of the main factors in the DPR process, viz., powder gradation, rolling speed and rolling gap, on the density and morphology of a green sheet were discussed by using an orthogonal experiment design followed by experimental verification. The influence of DPR parameters on the density of the green sheet is examined by a range analysis, which can reflect the sensitivity of influencing factors to the forming quality of the green sheet. The larger the range value is, the more sensitive the influencing factor is. This suggests that the quality of the green sheet is mainly influenced by particle gradation. The results show that the density of the resulting DPR green sheet with optimal parameters is mainly 7.5~8.0 g/cm3, reaches 80% of the theoretical density, and the mechanical strength can also afford the transferring process of the green sheet for the next sintering craft. The methods for modeling, obtaining physical parameters and the numerical simulation results can be used to guide rapid formation of the metal sheet by using direct powder rolling craft.

In current study; the effect of various Gadolinium (Gd) additions on the microstructure and sliding wear behaviour of Al-15%Mg2Si composite before and after the hot extrusion process was examined. Optical microscopy (OM), scanning electron microscopy (SEM) equipped with EDX facility and X-ray diffraction (XRD) were used to characterize the microstructure. The results showed that with addition of 1.0 wt.% Gd to Al-15%Mg2Si composite, the primary Mg2Si particles size reduced from 44 µm to 23 µm and its morphology altered from dendritic to polygonal shape. Further refinement of primary Mg2Si particles was achieved after conducting hot extrusion which resulted in a decrease in its size to 19 µm with a transfer to near-spherical morphology. The Vickers hardness value increased from 55.6 HV in the as-cast and unmodified composite to 72.9 HV in the extruded 1.0% Gd modified composite. The wear test results revealed that composites treated with Gd possess higher wear resistance in comparison with those of without Gd. The highest wear resistance obtained with the lowest wear rates of 0.19 mm3/km and 0.14 mm3/km in the Al-15%Mg2Si-1.0% Gd before and after the hot extrusion, respectively. The high wear resistance of extruded Gd-modified Al-15%Mg2Si composite is due to the refinement of primary Mg2Si particles with uniform distribution in the composite matrix along with fragmentation of Gd intermetallic compounds.

The precipitation and distribution behaviors of in situ-formed titanium boride whiskers (TiB) in TiBw-reinforced Ti-6%Al-4%V (Ti64) composites fabricated from an elemental mixture of Ti64 alloy powder and TiB2 particles by selective laser melting were investigated. The primary precipitation of TiB whiskers strongly depends on B content. For a B content of less than 2 mass%, when the liquid → β-phase transformation occurred and B atoms were discharged, the B-enriched area formed around the β-phase resulted in the generation of TiB whiskers and their agglomeration at the prior β-grain boundaries. When the B content was over 2 mass%, TiB whiskers directly precipitated from the liquid phase and moved to the molten pool boundary via Marangoni convection. As a result, the TiB whiskers were located along the boundary. Furthermore, B-enrichment caused a decrease in the liquidus temperature and thus obstructed β-grain coarsening, and as a result, fine equiaxed α’-grains formed during the phase transformation.

In the current study, the effect of different B4C additions (0, 2.5, 5, and 10 wt%) on the microstructural, solidification behavior, mechanical, and tribological properties of Al-20%Mg2Si composite were studied by means of scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Vickers hardness, tensile, and dry sliding wear tests. The cooling curve thermal analysis (CCTA) approach was utilized to monitor the influence of B4C particles on the solidification behavior of Al-20%Mg2Si composite. The results revealed that the addition of B4C particles up to 10 wt% reduced the nucleation temperature (TN) and growth temperature (TG) of the primary Mg2Si phase. Moreover, the proper amount of B4C added to Al-20%Mg2Si composite has a significant effect on the microstructural alteration, mechanical, and tribological properties of the composite. The mean size of primary Mg2Si in Al-Mg2Si composite was 47 μm, in which with the addition of 5 wt% B4C, the particle size decreased to 33 μm. The highest UTS (217 MPa) and El% (7%) was achieved in Al-20%Mg2Si-5%B4C hybrid composite. The cast Al-20%Mg2Si composite revealed the brittle mode of fracture with some cleavage characterization, in which with the addition of 5%B4C, the fracture mode altered to a more ductile fracture. The wear results revealed that the Al-20%Mg2Si-5%B4C hybrid composite has the highest wear resistance with the lowest wear rate (0.46 mm3/Km) and friction coefficient (µ = 0.52) under 20 N applied load compared to other fabricated composites with mild abrasion as the governed wear mechanism.

Ball milling (BM) is the prime method to disperse graphene into metal powders; however, it inevitably introduces structural defects to graphene. The balance between dispersion quality and structural damage of graphene during BM is a significant issue for fabricating graphene/metal composite powders. In this study two metal powder characteristics, namely type and size, were investigated to understand the effect of the BM process on graphene structure in graphene/metal composite powders. Graphene nanosheets (GNSs) were added into commercial Ti-6Al-4V and pure Al powders with different diameters by three kinds of BM processes with distinct energy levels. According to the microstructure and Raman spectra, the results suggested that metal particle size had a minor influence in low-energy BM, while it played an important role in high-energy BM (HEBM). The structural defects of GNS crystals increase with increasing BM energy. However, increasing energy in BM has limited damage as the discrepancy in particle size is quite large. Furthermore, Al powders with lower hardness tend to deform with lower BM effect, which will cause less damage to GNSs compared to that in the harder Ti powder. Those findings may have implications for the development of high-performance metal matrix composites reinforced with nanocarbon materials.

An Al3Zr-reinforced Al matrix composite using metal powders was fabricated via in-situ synthesis in vacuum; these were subjected to a pin-on-disc wear test with a SUS304 disc specimen under oil lubrication. The elemental mixture of Al and ZrH2 particles was sintered in vacuum for the in-situ-formed Al3Zr. ZrH2 particles were thermally decomposed in the reaction with the Al matrix to form hard Al3Zr intermetallic compounds. The friction coefficient and wear volume values of the Al–Al3Zr composites were significantly lower than those of the pure Al specimen. This is attributed to the uniform dispersion of Al3Zr particles in the Al matrix, which prevented the metallurgical bond from falling and blocked the direct contact between the Al matrix and SUS304 disc.

Zirconium effectively became an emerging alloying element used for titanium in order to improve its mechanical properties by Ti grains refinement and solid solution strengthening effects. As a result, Ti-Zr alloy enhances its industrial applications. In this study the titanium powders were sintered after the addition of 2.5 wt% of Zr using Spark Plasma Sintering (SPS) technology. The original pre-mixed powder consists of pure Ti and ZrH _2 particles. An applied pressure of 40 MPa and a short sintering time of 5 min were fixed in all experiments under a vacuum of 1 Pascal. EDS, XRD and XPS analysis showed that Zr dispersion as solid solution through α-Ti was homogenized for sintered samples at 1000 °C and 1200 °C while the agglomeration of ZrH _2 was detected in the sample sintered at 800 °C. These agglomerated particles reduced the average Zr content through titanium matrix compared to an average of 2.3 to 2.7 wt% for samples sintered at 1000 °C and 1200 °C. The hardness increases with the increase in the sintering temperature. However, since the sample sintered at 1200 °C showed an excessive grain growth that reduced its strength, it was found that 1000 °C sintering temperature can be an optimum temperature for this process.

Stents are one of devices for the invasive cardiac catheterization (Percutaneous Transluminal Coronary Angioplasty) and especially for pediatric catheterization, the stent is manufactured by superelastic alloys including TiNi alloy. Transradial coronary intervention (TRI) is an invasive treatment in comparison with transfemoral coronary intervention (TFI), as TRI can reduce the risk of bleeding complications. To perform TRI, it is necessary to reduce the thickness of stent and diameters of delivery system. Therefore, one of the solution is to improve the strength of the materials for the stent. In this study, the medical application to stents was investigated by manufacturing high-strengthened Ni-rich powder metallurgy TiNi alloy using pure Ti powder and pure Ti pre-mixed powder. Ni-rich TiNi shape memory alloys showed much high plateau stress and enough shape recovery rate compared to the conventional ingot metallurgy TiNi alloy used in the commercial stent devices. In the simulation of the stent radial force by a finite element analysis (FEA), it was clarified that the radial forces of Ti-52.0 at.%Ni (stent wall thickness; 80 μm) and Ti-50.5 at.%Ni (stent wall thickness; 200 μm) were equivalent. The improvement of plateau stress of TiNi alloys successfully reduced the thickness of the stent by 120 μm (60 %). In fact, the stent using Ni-rich TiNi alloy resulted in the thinned stent with a high radial expansion force. When implanting the stents made of Ni-rich TiNi alloy into the external iliac artery of pigs, no stent fracture was observed, and in-stent occlusion never occurred after 1-month and 3-month placement of the stents. They are similar biocompatibility to commercial stents because of the similar results of inflammation.

(TiCp + TiBw)/Ti composite was firstly prepared by spark plasma sintering (SPS) and hot extrusion from Ti-B4C system, and then isothermally heat treated at 400–800 °C for 24 h to study the pinning effect of the in situ formed reinforcements. Microstructure and phase composition was investigated by SEM, XRD and TEM, variation of the grain size of Ti matrix was studied by EBSD analysis, and room temperature strength was also measured after different heat treatments. Results show that, comparing with pure Ti materials, both the grain size of Ti matrix and the room temperature strength of the composite almost keep stable after heat treatments, suggesting the pinning effect of in situ formed TiCp and TiBw is effective to suppress the growth of Ti matrix grains during heat treatments.

Carbon nanotubes (CNTs) are promising reinforcements for fabricating aluminum (Al) matrix composites with outstanding properties. The understanding of the consolidation process of CNT–Al composite powders plays a significant role in achieving high performances of bulk composites. In this study, an advanced consolidation technique of spark plasma sintering (SPS) was used to fabricate CNT–Al composites with homogeneously dispersed CNTs. The sintering kinetics of pure Al powders and those powders coated with 1 wt % CNTs were studied. By combining the electrical conductivity and relative density results, it was found that the sintering process consisted of two stages with distinct densification rates. The second stage with a much lower rate was governed by the breaking down of alumina films at primary particle boundaries. The activation energy of the controlling second stage increased by 55% in CNT–Al composite powders compared to that of pure Al powder. As a result, CNT addition led to the overall decrease of sintering ability, which raised a challenge in the processing of CNT–Al composites.

For the evaluation of wear behavior of Mg composites under oil lubrication conditions, powder metallurgy Mg97Y2Zn1 alloy reinforced with additive Mg2Si particles were fabricated by the repeated plastic working (RPW) and hot extrusion. The RPW process was effective in refining both Mg2Si reinforcements and α-Mg grains causing the matrix hardening. When increasing the repetition number of RPW process from 200 to 600 cycles, the particle size of Mg2Si additives changed from 8 μm to 1~2 μm, and α-Mg grain size was 1 μm or less. With regard to the defensive and offensive properties of Mg alloys reinforced with Mg2Si dispersoids, the composite had superior adhesive wear resistance compared with the conventional Mg alloys because of its extremely high microhardness of 95~180 Hv by RPW process. The uniform distribution of refined Mg2Si particles was useful for improving both defensive and offensive properties against AZ31B counter disk specimens. The Mg2Si prominent dispersoids in the matrix were also effective in forming the oil grooves around them, and caused the low and stable friction coefficient. On the other hand, in the case of the composite containing coarse Mg2Si particles, severely deep scratches were given on the counter face of the AZ31B disk, and resulted in an unstable and high friction coefficient.

Zr-Cu amorphous films were prepared by radio-frequency (RF) magnetron sputtering on glass substrate using two kinds of the elemental composite targets: Cu chips on Zr plate and Zr chips on Cu plate. It was easy to precisely control chemical compositions of sputtered films by selecting the chip metal and the number of chips. It is possible to accurately estimate the film compositions by using the sputtered area and the deposition rate of Cu and Zr. XRD analysis on every as-sputtered film showed the broadened pattern. Zr-rich composition film, however, revealed a small peak at the diffraction angle of 2𝜃=35∘, and Cu-rich one indicated it at 2𝜃=43∘. TEM and electron diffraction analysis on the former also showed the main Zr ring patterns and its streaks. Zr-rich composition film with Cu content of 34 at% or less indicated a good corrosion resistance by salt spray test. On the other hand, Cu-rich version with 74 at% Cu or more was poor in corrosion resistance. This was because Zr was reactively passive, and caused the spontaneous formation of a hard non-reactive surface film that inhibited further corrosion than Cu.

The deformation-coordination ability between ductile metal and brittle dispersive ceramic particles is poor, which means that an improvement in strength will inevita- bly sacrifice ductility in dispersion-strengthened metallic materials. Here, we present an inspired strategy for developing dual-structure-based titanium matrix composites (TMCs) that achieve 12.0% elongation comparable to the matrix Ti6Al4V alloys and enhanced strength compared to homostructure composites. The proposed dual-structure comprises a primary structure, namely, a TiB whisker-rich region engendered fine grain Ti6Al4V matrix with a three-dimensional micropellet architecture (3D-MPA), and an overall structure consisting of evenly distributed 3D-MPA “reinforcements” and a TiBw-lean titanium matrix. The dual structure presents a spatially heterogeneous grain distribution with 5.8 μm fine grains and 42.3 μm coarse grains, which exhibits excellent hetero-deformation-induced (HDI) hardening and achieves a 5.8% ductility. Interestingly, the 3D- MPA “reinforcements” show 11.1% isotropic deformability and 66% dislocation storage, which endows the TMCs with good strength and loss-free ductility. Our enlightening method uses an interdiffusion and self-organization strategy based on powder metallurgy to enable metal matrix composites with the heterostructure of the matrix and the configuration of reinforcement to address the strength-ductility trade- off dilemma. [ABSTRACT FROM AUTHOR]