Hiroshi Izui

Densification, Microstructure, and Behavior of Hydroxyapatite Ceramics Sintered by Using Spark Plasma Sintering

This paper discusses the dependence of the mechanical properties and microstructure of sintered hydroxyapatite (HA) on the sintering temperature and pressure. A set of specimens was prepared from as-received HA powder and sintered by using a spark plasma sintering (SPS) process. The sintering pressures were set at 22.3 MPa, 44.6 MPa, and 66.9 MPa, and sintering was performed in the temperature range from 800°C to 1000°C at each pressure. Mechanisms underlying the interrelated temperature-mechanical and pressure-mechanical properties of dense HA were investigated. The effects of temperature and pressure on the flexural strength, Youngs modulus, fracture toughness, relative density, activation energy, phase stability, and microstructure were assessed. The relative density and grain size increased with an increase in the temperature. The flexural strength and Youngs modulus increased with an increase in the temperature, giving maximum values of 131.5 MPa and 75.6 GPa, respectively, at a critical temperature of 950°C and 44.6 MPa, and the fracture toughness was 1.4 MPa m 1/2 at 1000°C at 44.6 MPa. Increasing the sintering pressure led to acceleration of the densification of HA.

Sintering Performance and Mechanical Properties of Titanium Compacts Prepared by Spark Plasma Sintering

Titanium alloys were produced by blended elemental powder metallurgy (P/M) method. We focused on the effect of alloying elements (Fe, Mo, and Al) on the consolidation and mechanical properties of Ti compacts prepared by spark plasma sintering. The effects of amount of alloying elements and sintering temperature on the relative density and tensile properties of Ti compacts were investigated. The addition of β-stabilizing elements (Fe and Mo) significantly improved the densification of Ti compacts, where the relative density ratio of Ti-5 wt% Mo specimen became higher than 99.9 %, and Ti-5 wt% Fe specimen higher than 99.0 %. On the other hand, the addition of Al as α-stabilizing element led to improve the relative density of Ti-5 wt% Al compact with higher than 99.9 %. The tensile property for sintered Ti-5 wt% Mo compact had the highest elongation of 16 %. It will be discussed the microstructures and tensile property of the compacts.

Mechanical Properties of ZrO2 (Y2O3)-Al2O3 Nanocomposites with Addition of Hydroxyapatite Prepared by Spark Plasma Sintering

TZP-3Y20A/HA composites with addition of different volume fraction of hydroxyapatite (HA) were fabricated successfully using spark plasma sintering (SPS). The densification behavior and mechanical properties of composites are investigated as a function of sintering temperature and HA content respectively. The density of TZP-3Y20A composite increases steadily with temperature and a maximum value of 97.8% is obtained after sintering at 1400°C. Sintering the TZP-3Y20A/HA composites at 1400°C led to the decomposition of HA in the samples. Flexural strength, fracture toughness and Vickers hardness values increase with increasing sintering temperature, show decrease trend with increasing of HA content at the same temperature. They compared well with densities obtained at different sintering temperature. The maximum flexural strength, fracture toughness and Vickers hardness of 967.1 MPa, 5.27 MPam1/2 and 13.26 GPa were achieved for TZP-3Y20A composite respectively. Flexural strength, fracture toughness and Vickers hardness values of TZP-3Y20A/HA composite fell within the value range of dense HA and of TZP-3Y20A composite.

Effect of Alloying Elements on the Consolidation and Mechanical Properties of Ti Compacts by SPS

In this study, we focused on the effect of alloying elements (Fe, Mo, and Al) on the consolidation and mechanical properties of Ti compacts. The elemental blended powders is manufactured by spark plasma sintering. The effects of amount of alloying elements and sintering temperature on the relative density and tensile properties of Ti compacts were investigated. The addition of β-stabilizing elements (Fe and Mo) was found significantly improve the densification of Ti compacts, where the sintered density ratio of Ti-5 wt.% Mo specimen was higher than 99.9 %, and Ti-5 wt.% Fe specimen was higher than 99.0 %. On the other hand, addition of Al as α-stabilizing element showed the sintered density rate of Ti-5 wt.% Al specimen was higher than 99.9 %. The tensile property for sintered Ti-5 wt.% Mo specimens had the highest elongation of 16 %. It will be discussed the microstructures and tensile property of the compacts.

Effects of Surface Roughness of Base Metals on the Residual Stress of Filler Metals at Brazed Joints

The purpose of this study is to make clear some effects of surface roughness of the base metals on the residual stress of the filler metals at brazed joints. Although brazing and soldering techniques have been used in the mechanical industry as the metallurgical joining process for a long time, both techniques are still extensively applied to assemble electric circuits, electronic instruments and other precision machine parts. This paper presents some experimental data of the relationship between the surface roughness of the base metals (mild steel, SUS410, pure Titanium and Ti-6A1-4V) and residual stress of the filler metals (Ag-Cu eutectic alloy, Pd-Ag alloy and Pd-Cu alloy) at brazed joints using 7kW resistance vacuum furnace. Through the study we arrived at the following conclusions: the residual stress at the brazed joints of the specimens with coarse surface of the base metals have a higher value than that of one with smooth surface of the base metals. In the process its observed that the actual brazed area at the joint of the specimens with higher roughness has a higher stress value than that of one with smooth surface, that is, the shape factor value of the coarse roughness have the larger value than that of one with smooth surface of the brazed surface. And also, concerning the tensile strength of the brazed specimens, we have observed that the tensile strength of the brazed specimens with coarse surface have a higher value than that of one with smooth surface of the base metal. The above observation holds consistently for all the different materials used in this study.

Mechanical Properties and Wear Resistances of TiC or B4C Reinforced Ti-6Al-4V Prepared by Spark Plasma Sintering

Titanium and its alloys have excellent specific strength and corrosion resistance. However, they have a high initial cost and high machining cost, and poor wear resistance. Therefore, both factors should be considered in order to reduce the cost and improve the wear resistance of titanium alloy parts. Powder metallurgy (PM) has been taken into account for lowering the their costs. Titanium alloys reinforced with ceramic particle improves their wear resistance and hardness. In this study, we focus on the microstructures, mechanical properties, and wear resistance of TiC or B4C reinforced Ti-6Al-4V composites by using spark plasma sintering. The volume fraction of the reinforcement from 0 to 19.9 vol. %. The tensile strength of TiC/ and B4C/Ti-6Al-4V had 1058MPa (14.9 vol. % TiC) and 1095MPa (1.7 vol. % B4C), respectively. Vickers harnesses of TiC/ and B4C/Ti-6Al-4V increased with increase in the volume fraction of the reinforcement. The wear resistance of B4C/Ti-6Al-4V exhibited superior to that of TiC/Ti-6Al-4V.

Fabrication of Hydroxyapatite-incorporated ZrO2-20 wt% Al2O 3 by Spark Plasma Sintering and Characterization

Yttria-stabilized tetragonal zirconia/20 wt% alumina (TZP-3Y20A) composites were fabricated by spark plasma sintering at various sintering temperatures over the range of 1000—1400°C. Hydroxyapatite (HA) additive was added in volume fractions of 10—50% in order to increase the biocompatibility of the composite. The densification behavior of the TZP-3Y20A composite and that of the composites with HA were investigated. In the case of TZP-3Y20A composites, the density increases steadily with temperature and reaches a maximum value of 97.8% of the theoretical density at 1400°C. The solution interface formed between zirconia (ZrO2) and alumina (Al 2O3) strengthens the bond between ZrO2 and Al 2O3 grains and facilitates densification. In the case of TZP-3Y20A/HA composites, sintering at 1400°C led to the formation of tricalcium phosphate in the samples, which resulted from the decomposition of HA due to its limited thermal stability at high temperature; no reaction was observed between ZrO2 and HA. The addition of HA imposes a barrier effect on the diffusion between ZrO2 and Al2O3 grains, thus limiting the grain growth of ZrO2 and Al2O 3.

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.