Search

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.

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.

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.

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.

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.

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.

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.

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]

Aim. We aimed to develop a simulation dry model for endoscopic sphincterotomy (ES) and needle knife precut sphincterotomy (NKP) and to evaluate its usefulness as a training simulator. Materials and Methods. An endoscopic retrograde cholangiopancreatography trainer was used as a duodenum, bile duct, and papilla simulator. A simulated papilla was created with a piece of rolled uncured ham, and ES and NKP were performed. Hands-on training was carried out using this model, and success and failure of the procedures were evaluated. A questionnaire survey was conducted among the participants to assess the performance and usefulness of the dry model for ES and NKP training. Results. Twenty-two endoscopists participated in the hands-on training using this dry model. ES was successful in 33 out of 34 attempts (97%) whereas NKP was successful in all 7 attempts (100%). Based on the results of the questionnaire survey, the median score for realism was 7 (range: 2–9) for ES and 8 for NKP on a scale of 1 to 10. Conclusions. The dry model using an uncured ham provides a condition closely similar to actual clinical practice and is useful as a training model for ES and NKP.