Effect of Manufacturing Process of Master Alloy Powders on Homogeneity of Sintered Ti-5Al-1Fe by Blended Elemental Powder Metallurgy

To narrow down the candidates of the alloying element powders for Ti-5Al-1Fe products manufactured with BE/PM, two master alloy powders, atomized spherical 5Al-1Fe and crushed-andground polyhedron 5Al-1Fe-4Ti ternary powders, were investigated with emphasizing on homogeneity of alloying elements, Al and Fe, in sintered Ti-5Al-1Fe. Intense Al segregation is recognized in the sintered specimen manufactured using 5Al-1Fe atomized powders, while strong segregation is not observed in the specimen manufactured using 5Al-1Fe-4Ti crushed-and-ground powders. Density of sintered specimen manufactured using 5Al-1Fe atomized powders is lower than that manufactured using 5Al-1Fe-4Ti crushed-and-ground powders. Al segregation and lower sintered density are probably caused by lower density of the powder substance, high flowability of spherical powders and phase constitutions some of which have low melting points. Those factors have to be taken into account to manufacture sintered titanium alloys with high homogeneity by BE/PM.

Effect of Sintering Temperature on the Mechanical Properties of Nanostructured Zirconia Fabricated via Colloidal Processing

This study aims to evaluate the effects of sintering temperature on the density and hardness of tetragonal zirconia polycrystals stabilized with 3 mol% 3Y-TZP dental ceramic type. Five cylindrical specimens were fabricated from zirconia powder of particle size 50 nm via colloidal processing. The specimens were sintered densely at the final sintering temperatures of 1000, 1100, 1200, and 1300 °C, respectively. The sintered density and hardness of the sintered specimen were then examined. The results showed that the sintered densities and hardness of the specimen increased as the temperature increased from 1000 °C to 1300 °C. Zirconia 3Y-TZP could gain near full density and reach hardness of as high as 11.30 GPa at the final sintering temperature of 1300 °C. The density and hardness of zirconia structured from 3Y-TZP can be improved by controlling the final sintering temperature.

Dissolution Resistance of Bovine Teeth-Derived Hydroxyapatite

Dissolving behavior of hydroxyapatite ceramics prepared from bovine teeth (BTHA) was investigated. The bovine teeth were soaked in 0.1 M of NaOH at 80°C for 1 h. After soaking, the teeth were calcined at 800°C for 1 h, and then they were attritor-milled for 24 h. BTHA powder consisted of mainly HA and small amount of MgO. The powders obtained were cold isostatically pressed and sintered at 1200°C with a dwell time of 1 h. Sintered density of BTHA was about 70%. After polishing the surface of sintered specimen, BTHA was immersed in buffered water at 37°C for 3 and 7 days. After immersion period, there is no evidence of dissolution for BTHA at the end of the immersion time. In addition, there is no change of peak intensity in XRD after immersion time. It was found that hydroxyapatite from bovine teeth was more stable than commercial HA in liquid environment.

Corrosion Behavior of some Sintered CuNi Alloys – Preliminary Laboratory Data

The paper aims to discuss some aspects on corrosion behavior of specimens from sintered CuNi alloys (e.g. Cu90Ni10; Cu70Ni30). The above mentioned specimens were manufactured by dissimilar laboratory routes: from alloyed powders, from elementary powders and from mixtures consisting of Cu80Ni20 alloy and an alloying element. Research aims to establish the manufacturing parameters influence on sintered specimens characteristics (density, porosity, microstructure features) in order to correlate them with corrosion tests laboratory data. There were investigated the corrosion mechanisms in relation with macro- and microstructure properties of the sintered specimen surface. For comparison purposes, it is intended to extend the analysis to Cu60Ni40 and Cu80Ni20 sintered alloys.

Fabrication of Al-Si-Cu-Mg-Zn Alloy Matrix Composite Reinforced with Submicrometer Sized Al2O3 Particles Formed by Displacement Reaction

The displacement reaction (in situ reaction) is an effective process to solve the interfacial problem between Al matrix and ceramic particles in Al alloy matrix composites. In this study, an Al alloy matrix composite powder containing nanometer was produced by using high energy ball milling, and a bulk Al alloy matrix composite reinforced with nanometer and submicrometer sized Al2O3 particles was obtained by sintering the ball milled composite powder at 950 °C for 2h. It was found that the Al2O3 particles were homogeneously distributed in the Al matrix after sintering. Some of the Si particles have lots of fine Al2O3 particles distributed homogeneously in the Al matrix. The hardness of the sintered specimen produced using as-milled composite powder is higher than that of the sintered specimen produced using as-mixed powder.

Pulsed Electric Current Sintering of Nano-Crystalline Iron-Base Powders

A new process of pulsed electric current sintering was developed. It combines compaction with activated sintering effectively and can manufacture bulky nano-crystalline materials very quickly. Pulsed electric current sintering of high-energy ball-milled nano-crystalline iron-based powders is investigated in this work. A nanostructured steel is obtained with high relative density and hardness by this process. The average grain size of iron matrix is 58nm and the carbide particulate size is less than 100nm. The densification temperature of ball-milled powders is approximately 200°C lower than that of blended powders. When the sintering temperature increases, the density of as-sintered specimen increases but the hardness of as-sintered specimen first increases and then decreases. Microstructure analysis results show that the decrease of hardness is caused by the dramatic grain growth of iron matrix.

RESEARCH ON SHAPING TECHNOLOGY OF NANOCOMPOSITE WC-6Co POWDER AND PROPERTIES OF SINTERED COMPACTS

The influences of powder extrusion molding (PEM), die pressing and cold isostatic pressing (CIP) on the green compacts and the sintered compacts of nanocrystalline WC-6 Co composite powder produced by spray pyrogenation-continuous reduction and carburization technology were researched. The results showed that the pore volume distribution, density and scanning electron microscopy (SEM) morphologies of fractured surface of powder extrusion molding or die pressing followed by the cold isostatic pressing consolidation green compacts were better than that of powder extrusion molding or die pressing. The green compacts were sintered by using vacuum sintering plus hot isostatic pressing (HIP), the sintered specimens were characterized by testing density, Rockwell A hardness, saturated magnetization, coercivity force, transverse rupture strength (TRS) and atomic force microscope (AFM) images, the results showed that sintered specimen of the green body that prepared by powder extrusion molding or die pressing followed by cold isostatic pressing had excellent properties of high strength and high hardness, transverse rupture strength of sintered specimen was more than 3100 MPa, Rockwell A hardness of sintered body was more than 93. Ultrafine WC-6 Co cemented carbide rods with excellent mechanical properties and fine microstructure were obtained.

'The Role of the Grain Boundary on the Resistivity of Pb(Fe1/2Nb1/2)O3 at Room Temperature

The effect of changing sintering temperature on the grain boundary properties and the room temperature resistivity (ρRT) of Pb(Fe1/2Nb1/2)O3 (PFN) was investigated. Monitering the temperature dependence of resistivity showed that the ρRT's of 1050°C and 1150°C-sintered specimen were 1011ΩEcm and 104ΩEcm respectively, but the resistivity above 300°C became nearly identical. The previous model, that the low resistivity of PFN is due to the electron hopping between Fe2+ and Fe3+ driven by the reduction of PFN, couldn't explain this phenomenon, and the reconsideration of the Fe reduction revealed that the difference of electron concentration between the 1050°C and 1150°C-sintered specimen couldn't exceed one order of magnitude. The role of the grain boundary was introduced in order to account for this phenomenon.