Comparison of sintering of titanium and titanium hydride powders

Abstract

The cold compaction and vacuum sintering behaviour of a Ti powder and a Ti hydride powder were compared. Master sintering curve models were developed for both powders. Die ejection force, green strength and green porosity were lower for hydride powder than for Ti powder, all probably resulting from reduced cold welding and friction during compaction. For sintering temperatures above ～1000°C, most of the difference in the sintered density of Ti and hydride is explained by assuming equal densification, while taking into account the lower green porosity of compacts made from hydride powder. However, there is evidence that particle fracture during compaction also contributes to increased sintered density for hydride powder. The Ti powder conformed to a master sintering curve model with apparent activation energy of 160 kJ mol^?. The activation energy for Ti hydride also appeared to be about 160 kJ mol^?, but the model did not fit the experimental data well.     

氢化钛粉颗粒的粉碎及机理研究

本文采用闭环气流磨系统对氢化后得到的粗颗粒氢化钛粉进行粉碎,利用扫描电子显微镜和粒度分析技术对结果进行表征,并对闭环气流磨的粉碎机理进行了讨论。结果表明,对粗颗粒氢化钛粉进行闭环气流磨粉碎,克服了氢化脱氢法(hydrogenation dehydrogenation,HDH)制备的钛粉存在的粒度不均匀、粒度分布较宽等品质问题;其粉碎机理可总结为,经多股高速高压氩气流冲击、打磨,粉末颗粒自身相互碰撞、摩擦,以及粉末颗粒与磨料腔腔壁、分级轮的碰撞,粗颗粒氢化钛粉从大颗粒粉碎成细小颗粒。     

Swelling during sintering of titanium alloys based on titanium hydride powder

Abstract

Compacts were prepared by pressing titanium and titanium hydride powders mixed with nickel powder and sintering under vacuum. Severe swelling was observed only for compacts based on TiH₂ powder. Pressure changes in the vacuum furnace, dilatometry results and mass loss data all indicate that dehydrogenation of TiH₂ powder compacts occurs at lower temperature than any significant sintering. Swelling appears to have been caused by a contaminant in the TiH₂ powder rather than hydrogen. The onset of severe swelling during heating was associated with the formation of liquid phase as the solidus was crossed. However, some swelling appears to take place under solid state sintering conditions. Various results indicate that the mechanism of swelling is high gas pressure within closed pores. Large pores appear to form by breakage of ligaments between small pores followed by opening of the pore. It appears that the use of (uncontaminated) TiH₂ powder in place of Ti powder would allow the benefit of lower green porosity to be retained during sintering to achieve low sintered porosity.     

闭环气流磨粉碎氢化钛粉

随着钛及钛合金粉末冶金技术的快速发展,采用氢化钛粉代替钛粉作为主要原料制备粉末冶金钛材料已成为国内外的研究热点。本文研究了闭环气流磨系统粉碎氢化钛的工艺过程及特点,并采用SEM、化学分析以及激光粒度测试分析等表征所制备氧化钛粉的形貌、氧含量及粒度分布。结果表明:氢化钛经闭环气流磨后,粒度(D_(50))达到5.94μm;不同粒径(粉末粒径分别为250,150,75和48μm)的氢化钛粉在闭环气流磨分级轮频率为200Hz下,粒度(D_(50))达到10μm以内,且粒度分布区间较窄;而同一粒径(250μm)的粉末在闭环气流磨不同分级轮频率下(80,100,120,140,160,180和200 Hz)分级后,粉末的粒度(D_(50))和粒度分布区间随分级轮频率的降低而增大和变宽;因为闭环气流磨系统是封闭的循环回路,采用高纯氩气作为磨料介质,因此物料粉碎前后的增氧量低。     

氢化钛的动态分解行为与规律

通过DSC/TG的热分析试验,研究氢化钛升温过程中分解的动力学规律,利用Coast-Redfern积分法计算了分解过程的动力学参数。结果表明,氢化钛热分解的开始温度为510℃,分解过程中总质量损耗率达3.15%,其中565～660℃温度范围内的质量损耗率占总质量损失的50%左右,分解过程中生成了比氢化钛热稳定性更高的TiHx(0.7相似文献   

Porous titanium processed by powder injection moulding of titanium hydride and space holders

Abstract

Biocompatibility, bone-like mechanical properties, and good bone-to-implant anchorage are current requirements for permanent implants. Porous titanium can satisfy these requirements provided that sufficient porosity, large enough pores and interconnections allowing bone ingrowth can reliably be obtained with controlled processes. In the present work, porous parts are processed from titanium hydride based feedstocks containing space holders. Two formulations have been developed: a feedstock with a polyethyleneglycol based binder and NaCl space holders, and a feedstock with a paraffin based binder and PMMA space holders. Depending on the sintering conditions, porosity levels between 30 and 60% and open porosity between 10 and 40% are obtained, with pore sizes in the range 50–500 μm. The microstructure, porosity and mechanical properties of porous titanium sintered at various temperatures have been characterised by scanning electron microscopy and compression tests.     

Use of titanium hydride for the synthesis of titanium aluminides from powder materials

Titanium aluminides Ti₃Al and TiAl were synthesized by the use of TiH₂+Al powder mixtures. Phase transformations occurring upon the decomposition of titanium hydride in vacuum and inert gas and synthesis of titanium aluminides were studied. It was shown that the use of titanium hydride instead of titanium in powder mixtures with aluminum results in a significant activation of diffusion processes, and leads to an accelerated production of single-phase titanium aluminides upon isothermal heating. This is attributable to the small particle size of the charge, high density of defects (including those due to hydrogen-phase hardening) in the titanium and aluminum lattices, and possible reduction of Al₂O₃ films by atomic hydrogen. The type of atmosphere did not noticeably effect the rate of phase formation, however synthesis in vacuum appears to be more practical since hydrogen is completely removed with simultaneous formation of the aluminides. Due to the fact that aluminum reacted completely with titanium in the solid state, final products close to theoretical densities were obtained without the application of high pressure.     

Production of titanium grade 4 components by powder injection moulding of titanium hydride

Abstract

Recent developments are presented on powder injection moulding of titanium from metal hydride powders and binders composed of polyethylene, paraffin wax and stearic acid. The feasibility of using this route to process fit for purpose, complex parts is assessed. Titanium hydride offers a low cost solution compared with pure titanium powders. Feedstocks for powder injection moulding were prepared in a sigma mixer. Tensile test specimens and demonstration parts were injection moulded. Solvent debinding in heptane was followed by thermal debinding and dehydrogenation under argon. Titanium parts were sintered at 1200°C under argon. Sintered parts exhibit a linear shrinkage of about 20%, good shape preservation and reproducibility. The yield strength (519 MPa), ultimate tensile strength (666 MPa), elongation to fracture (15%) and interstitial content measured by quantitative analysis meet the requirements for titanium grade 4.     

Mass-spectrometeric quantitative analysis of thermal dissociation of titanium hydride

Translated from Poroshkovaya Metallurgiya, No. 12(312), pp. 62–64, December, 1988.     

氢化钛氧化处理及其热分解行为

在大气条件下进行氢化钛的氧化处理试验,利用扫描电镜和X射线衍射仪研究氧化处理后氢化钛的形貌与相组成,通过TG/DSC热分析,研究氧化处理对氢化钛热分解行为的影响规律。结果表明,氧化处理后氢化钛颗粒形貌无明显变化,随温度升高和时间延长,其颜色经历了灰黑色—蓝色—浅灰色的转变,且颗粒表面形成了Ti3O和TiO2的氧化物薄膜。与此同时,随氧化处理温度升高和时间延长,氢化钛热分解的质量损失率降低,但氢化钛的热分解温度显著提高,以AlSi12合金为基体,应用粉末冶金法制备泡沫铝,其氢化钛的氧化处理工艺为480℃/1h。