Yoshiki Komiya

Experimental Optimization of Dry Sliding Wear Behavior of Titanium Matrix Composites Using Taguchi Methods

Titanium and its alloys have high specific tensile strength and exhibit poor wear resistance. To improve their wear resistance, ceramic-particulate reinforced titanium matrix composites (TMCs) are fabricated by a spark plasma sintering process (SPS). The wear behavior of the TMCs depends on various factors, such as the matrix and reinforcement materials, reinforcement volume fraction, applied load, sliding load, sliding distance, and sliding velocity. The influencing factors on the wear behavior of TMCs in Taguchi methods are classified as either noise factors or control factors. Noise factors include load, sliding velocity, and sliding distance, and control factors include type, shape, particle size of matrix material, type of reinforcement material, and reinforcement volume fraction. In this study, the control factors were selected for optimization by Taguchi methods. Experiments were conducted systematically based on an L18 orthogonal array of the methods. Wear tests were carried out using a three-ball-on-disk machine. The results indicated that the wear behavior of TMCs was affected by three factors, namely, the type of reinforcement material, the reinforcement volume fraction, and the type of matrix material, but was not affected by two factors, namely, the shape of the matrix material and the particle size of the matrix material. An Si3N4-reinforced hydride-dehydrate Ti matrix composite with 10 vol.% reinforcement showed good wear resistance.

Effect of Matrix and Reinforcement Powder Types on Tensile and Wear Properties of TiB/Ti and TiC/Ti Composites Prepared by SPS

Titanium and its alloys have low density, high specific strength, high fatigue strength, and good corrosion resistance. However, today they are underutilized in industry due to their high cost and poor wear resistance. To further improve their properties, TiB- and TiC-reinforced Ti matrix composites (TiB/Ti and TiC/Ti) were produced by the spark plasma sintering (SPS) process. The TiB and TiC distributions in the composites strongly affected their mechanical properties. We focused on how the matrix powder morphology and size affected their properties. Hydride-dehydride (HDH) and gas-atomized (GA) pure Ti powders with different powder sizes were used as a matrix, and TiB2 or TiC powders were used as a reinforcement. We investigated the microstructures, the tensile properties, and the Vickers microhardnesses of the composites. The ultimate tensile strengths and the Vickers microhardnesses of the composites containing smaller HDH powders were higher than those containing GA powders.

Mechanical Properties of TiB-Reinforced Ti-6Al-4V Using Matrix Powders with Different Particle Sizes and Morphologies

It has been reported that TiB is one of the most effective reinforcement materials. In this study, TiB-reinforced Ti alloys were sintered by using spark plasma sintering (SPS). Compared with the conventional method, SPS can sinter for a short period of time and at low temperature. TiB is produced by TiB2 and Ti in the composite during sintering. Three types of Ti-6Al-4V matrix powders were used: hydride-dehydride powders with particle diameters of 45 µm and 25 µm and gas-atomized powder with a particle diameter of 45 µm. TiB-reinforced Ti-6Al-4V alloys were prepared from these powders by SPS. The mechanical properties of the alloys did not depend on the particle sizes but depended on the particle morphologies.

Fabrication of Iron-Base Shape Memory Alloy Fiber Reinforced Aluminum by Spark Plasma Sintering

Aluminum was composited with iron-base shape memory alloy (SMA) fiber. It is important to join between matrix metal and reinforced SMA fiber successfully. Matrix metal can obtain compressive residual stress caused by shape memory effect of SMA fiber without strong interface. In this study, aluminum matrix composite reinforced by iron-base SMA fiber was fabricated by Spark Plasma Sintering (SPS). At this method, sintering of hard-to-sinter materials (Al and Ti), junction of flame bonding materials is easy. The pure aluminum powder with iron-base SMA fiber was joined at 773K. As a result, intermetallic phase was formed at the interface between aluminum and iron-base SMA fiber and it was clarified that the interfacial strength depends on kind and thickness of intermetallic phase. This strong interface gives beneficial residual stress into aluminum from SMA fiber.

Micromechanics-based Study on Thermo-mechanical Behavior of ZrO2/Ti Functionally Graded Materials

The aim of this study is to investigate thermo-mechanical response of ZrO 2 /Ti functionally graded materials (FGMs) fabricated by spark plasma sintering (SPS) based on a mean-field micromechanics model, which takes account of micro-stress relaxation due to interfacial diffusion between ceramic and metal phases as well as creep of both phases. A resistance to cyclic thermal shock loadings of FGMs with different compositional gradation patterns including Ti-rich, linear and ZrO 2 -rich gradation patterns has been investigated. The results demonstrate that Ti-rich FGMs show superior properties among the tested FGM samples. Mean-field micromechanics-based examinationsreveal that the range and ratio of thermal stresses in ZrO 2 surface layers in FGMs can affect cyclic thermal shock fracture behaviour but not mean thermal stresses. Creep of ZrO 2 have a large influence on dependence of the range and ratio of thermal stresses in ZrO 2 surface layers on compositional gradation patterns in the FGMs.

Effect of compositional gradient on mechanical properties in aluminum/duralumin multi-layered clad structures

This study aims to investigate the effect of compositional gradient on nano-, micro- and macro-mechanical properties in aluminum (A1050)/ duralumin (A2017) multi-layered clad structures fabricated by hot rolling. Such multilayered clad structures are possibly adopted to a new type of automobile crash boxes to effectively absorb the impact forces generated when automobiles having collisions. 2- and 6-layered clad structures with asymmetric lay-ups from one side of aluminum to another side of duralumin have been fabricated, which have been suffering three different heattreatments such as (1) as-rolled (no heat-treatment), (2) annealed at 400°C and (3) homogenized at 500°C followed by water quenching and aging (T4 heat treatment). For nano- and micro-scale mechanical properties proved by nanoindentation, higher hardness and elastic modulus correspond to higher Cu content at the interface in annealed and aged samples. For macro-scale mechanical properties, internal friction of 2-layered clad structures is higher than that of 6-layered clad structures in any heat-treatment samples. Deep drawing formability of annealed samples is considerably high compared to as-rolled and aged ones.

Microstructure Refinement of Pure Aluminum by Inoculation with Stainless Steel Powders

The aim of this study is to investigate efficiency of stainless steel powder inoculation into pure aluminum for microstructure refinement. Refiners consisting of pure aluminum powder (powder size: 106~180m) and stainless steel powder (powder size: 25~53m) have been fabricated through spark plasma sintering (SPS). The stainless steels used in the study include SUS304L, SUS316L and SUS434L. SUS 304L powder has achieved a great grain refinement in cast aluminum, for which fading phenomenon has been considerably avoided. SUS316L and SUS434L powders develop fine dendrite structures, which can lead to high hardness of cast aluminum.