Structure and properties of plasmochemical powders of aluminum oxide

Using modern methods of analysis, investigations of the phase composition, structure, and properties of powders of aluminum oxide synthesized by the plasmochemical method are carried out. The possibility of plasmochemical technology of treatment of dispersed raw materials for obtaining submicrometer and nanodimensional particles of aluminum oxide is shown.     

纳米AlN粉末的低温热压

研究了纳米AlN陶瓷在1 500~1 700℃的低温热压行为和力学性能.热压温度为1 600℃时,产物是β-AlN和β-Al2O3两相共存;当温度提高至1 700℃后,热压过程中出现由β-AlN到α-AlN相的转变.随着热压温度的提高,断裂形式由沿晶断裂逐渐向穿晶断裂转变,致密度逐渐提高,晶粒尺寸长大;当热压温度达到1 700℃时,相对密度为97.3%,晶粒平均直径为850nm,硬度值为15.54GPa,断裂韧度为3.5 MPa·m1/2.     

真空烧结温度对铜基减磨材料性能的影响

以铜粉、锡粉、铅粉等为原料,采用“压制-烧结”工艺制备了铜基减磨材料,烧结采用真空无压烧结和还原气氛保护烧结两种工艺方法.运用对比试验的方法,探讨了真空无压烧结工艺中不同烧结温度对铜基减磨材料烧结体性能的影响.结果表明:真空烧结工艺与还原气氛保护烧结工艺相比,相同的烧结温度下材料的孔隙度、抗拉强度、抗压强度和硬度变化不...     

ZrO2和结合剂对烧成镁钙砖烧结性能的影响

研究了电熔氧化锆、单斜氧化锆和两种结合剂（无水无羟基树脂和液体石蜡）对烧成镁钙砖烧结性能的影响。结果表明：作结合剂用时无水无羟基树脂效果好于液体石蜡；作为添加剂时电熔氧化锆和单斜氧化锫均能显著促进镁钙砖的烧结，其中单斜氧化锆的效果好于电熔氧化锆。加入的ZrO2与CaO反应生成了CaZrO3，存在于主晶相的晶界中，为离子扩散提供了迁移的途径，从而促进了烧结。     

真空烧结温度对WC-TiC-TaC-Co硬质合金组织和性能的影响

采用高能球磨、真空烧结工艺制备WC-13(TiC+TaC)-8Co-1(VC+Cr3C2)硬质合金,研究了不同烧结温度对WC-TiC-TaC-Co硬质合金微观组织、力学性能和磁性能的影响。结果表明,提高烧结温度有利于提高合金的致密度,但是过高的烧结温度会导致晶粒长大,使合金致密度下降;合金的硬度、抗弯强度和矫顽力随着真空烧结温度的提高先增大后减小;相对磁饱和强度随着烧结温度的升高呈现下降的趋势;1 400℃烧结的合金综合性能较好,合金的相对密度99.6%、抗弯强度1 992 MPa,硬度92.3 HRA,矫顽力34.3 k A/m,相对磁饱和强度为76.5%。     

Selective laser sintering of steel powders to obtain products based on SAPR-models

Conclusions  

Fine-grained tungsten-cobalt hard alloys based on plasmochemical tungsten

Translated from Poroshkovaya Metallurgiya, No. 4, pp. 42–46, April, 1992.     

Cyclic sintering of cermet powders

Summary It is shown that after eleven cycles of sintering under conditions of 1200–800 °C a stage of porosity stability of the sample sets in, and a stage of exhaustion of shrinkage.Cyclic sintering has no advantages over isothermal sintering: with equal temperatures and summary durations during sintering, the magnitude of porosity of the samples is the same.     

Influence of atmosphere on sintering of T15 and M2 steel powders

The sintering behavior of T15 and M2 water-atomized high-speed steel powders under vacuum and N₂-H₂-CH₄ atmosphere is analyzed. Sintering under the gas mixture allows high densities [99 to 100 pct total density (TD)] to be obtained at temperatures 45 to 50 K lower than for vacuum sintering for steel T15, but the high densities are reached at slightly higher temperatures (15K) than for vacuum sintering for steel M2. Chemical analysis of gas-sintered specimens has shown that a higher amount of nitrogen is absorbed during sintering of steel T15 (0.72 to 0.78 pct) than in the case of steel M2 (0.34 to 0.38 pct). Although MC and M₆C primary particles are observed during vacuum sintering, in gas sintering, the MC carbides change to MX carbonitrides. These particles are very fine (1 μm) and are very resistant to coarsening during oversintering. Sintering in the gas atmosphere allows important oversinterings (up to 50 K above the minimum sintering temperature for achieving a density higher than 99 pct of theoretical density) to be reached in the case of steel T15 without the formation of eutectic films. In the case of M2 steel, for gas sintering, the eutectic films appear for oversinterings smaller or equal to those for vacuum sintering.     

沉淀剂对ZrO_2(MgO)纳米粉体制备的影响

以ZrOCl_2·8H_2O、Mg(NO_3)_2·6H_2O为原料,分别以氨水、氨水+0.5 mol/L碳酸铵、氨水+0.5 mol/L碳酸氢铵为沉淀剂,采用化学共沉淀法制备ZrO_2(MgO)前驱体粉体.通过差热分析、X射线衍射、扫描电镜、红外光谱等对所得纳米粉体进行测定分析.结果表明:采用不同沉淀剂制得的ZrO2(MgO)纳米粉体平均晶粒尺寸都稍大于30 nm,用氨水+碳酸铵、氨水+碳酸氢铵为沉淀剂时,能够提高ZrO_2(MgO)纳米粉体的分散性能.     

Phase composition and mechanical properties of a zirconium dioxide based ceramic obtained by high temperature sintering in a vacuum

Changes in phase composition and mechanical properties of sintered ZrO₂ + 3% (mole) Y₂O₃ specimens were examined after annealing in air and after various mechanical operations. Compacted ceramic specimens containing T and T′ phase were obtained by sintering in a vacuum at 1800°C. Ceramics containing T and T′ phases have excellent toughness (K_1c up to 15 MPa·m^1/2), bend strength up to 800 MPa and HV hardness up to 13 GPa.     

Supersolidus liquid-phase sintering of prealloyed powders

A model is derived for the sintering densification of prealloyed particles that form internal liquids when heated over the solidus temperature. The model considers the powder size, composition, and microstructure, as well as the processing conditions of green density, heating rate, maximum temperature, hold time, and atmosphere. Internal liquid forms and spreads to create an interparticle capillary bond that induces densification during sintering. Densification is delayed until the particles achieve a mushy state due to grain boundary wetting by the internal liquid. This loss of rigidity and concomitant densification of the semisolid particles depends on the grain size and liquid quantity. Viscous flow is the assumed densification mechanism, where both viscosity and yield strength vary with the liquid content and particle microstructure. Densification predictions are compared to experimental data, giving agreement with previously reported rapid changes in sintered density over narrow temperature ranges. The model is tested using data from steels and tool steels of varying carbon contents, as well as boron-doped stainless steel, bronze, and two nickel-based alloys.     

Driving force for low temperature sintering of interstitial and intermetallic powders and induced applications

Abstract

Intermetallic as well as (carbides and nitrides) interstitial compounds present functional and structural properties which make these materials necessary for advanced technologies. Meanwhile fabrication routes based on melting and casting or plastic deformation, are usually far to compete with powder metallurgy processes likely to provide near net shaped parts and components. The present study is devoted to a model system exemplified by nitrided iron and steel powders for which the thermal stability of nitrides is severely decreasing when temperature exceeds critical values during densification treatments. Thanks to the analysis of the thermal treatment induced transformations mainly characterised by Mössbauer spectroscopy, the consequences and impact on driving forces for densification under critical thermal conditions are discussed in order to achieve an optimised sintering process and an actual development.