Oxygen variation in titanium powder and metal injection molding

The control of oxygen is paramount in achieving high-performance titanium(Ti)parts by powder metallurgy such as metal in-jection molding(MIM).In this study,we purposely selected the Ti and Ti-6Al-4V powders as the reference materials since these two are the most representative Ti materials in the industry.Herein,hydride-dehydride(HDH)Ti powders were pre-oxidized to examine the ef-fect of oxygen variation on the characteristics of oxide layer on the particle surface and its resultant color feature.The results indicate that the thickness and Ti oxide level(Ti^(0)→Ti^(4+))of the oxide layer on the HDH Ti powders increased as the oxygen content increased,lead-ing to the transition of color appearance from grey,brown to blue.This work aids in the powder feedstock selection at the initial stage in powder metallurgy.In addition,the development of oxygen content was comprehensively studied during the MIM process using the gas-atomized(GA)Ti-6Al-4V powders.Particularly,the oxygen variation in the form of oxide layer,the change of oxygen content in the powders,and the relevant parts were investigated during the processes of kneading,injection,debinding,and sintering.The oxygen vari-ation was mainly concentrated in the sintering stage,and the content increased with the increase of sintering temperature.The variation of oxygen content during the MIM process demonstrates the crucial role of powder feedstock and sintering stage in controlling oxygen con-tent.This work provides a piece of valuable information on oxygen detecting,control,and manipulation for the powder and processing in the industry of Ti and its alloys by powder metallurgy.

Phase Behaviors in Bi-phase Simulation of Powder Segregation in Metal Injection Molding

Powder segregation induced by mold filling is an important phenomenon that affects the final quality of metal injection molding （MIM）. The prediction of segregation in MIM requires a bi-phase flow model to describe distinctly the flows of metallic powder and polymer binder. Viscous behaviors for the flows of each phase should hence be determined. The coefficient of interaction between the flows of two phases should also be evaluated. However, only viscosity of the mixed feedstock is measurable by capillary tests. Wall sticking is supposed in the traditional model for capillary tests, while the wall slip is important to be taken into account in MIM injection. Objective of the present paper is to introduce the slip effect in bi-phase simulation, and search the suitable way to determine the viscous behaviors for each phase with the consideration of wall slip in capillary tests. Analytical and numerical methods were proposed to realize such a specific purpose. The proposed method is based on the mass conservation between the capillary flows in mono-phase model for the mixed feedstock and in bi-phase model for the flows of two phases. Examples of the bi-phase simulation in MIM were realized with the software developed by research team. The results show evident segregation, which is valuable for improving the mould designs.

Injection molding of micro-porous titanium alloy with space holder technique

The powder space holder （PSH） and powder injection molding （PIM） methods have an industrial competitive advantage because they are capable of the net-shape production of micro-sized porous parts. In this study, micro-porous Ti6Al4V alloy （Ti64） parts were produced by the PSH-PIM process. Ti64 alloy powder and spherical polymethylrnethacrylate （PMMA） particles were used as a space holder material. After molding, binder debinding was performed by thermal method under inert gas. Debinded samples were sintered at 1250℃ for 60min in a vacuum （10-4 Pa）. Metallographic studies were conducted to determine densification and the corresponding microstructural changes. The surface of sintered samples was examined by SEM. The compressive stress and elastic modulus of the rificro-porous Ti64 samples were determined. The effects of fraction of PMMA on the properties of sintered micro-porous Ti64 alloy samples were investigated. It was shown that the fraction of PMMA could be controlled to affect the properties of the Ti alloy.

Sintering products molded by injecting ceramic and metal powders

The injection molding products with different volume ratios of ZrO2 ceramic powder to 316L stainless steel powder were prepared. Properties and structure of the products were characterized by X-ray diffraction（XRD）, scanning electron microscope（SEM） and transmission electron microscope （TEM）. The results show that the compressive stress exists in the products and the bend strength reaches 300MPa. ZrO2 phase and stainless steel phase are uniform in samples. The toughness of ceramic increases with the increasing the content of stainless steel. Through TEM study of the interface, some crystalline orientation relationships are determined.

Rheological, mechanical and corrosive properties of injection molded 17-4PH stainless steel

The feedstock based on the binder 65%PW-30%EVA-5%SA has the best general rheological properties for the 17-4PH stainless steel powder. The 17-4PH stainless steel compacts sintered at 1 380 ℃ for 90 min have the best mechanical properties and the good microstructure with homogeneously distributed pore structure and the moderate-sized grains. Whereas the compacts sintered for 60 min and 120 min show an inadequate and an over-sintered microstructure respectively. The compacts sintered at 1380 ℃ for 90 min have the density of 7.70 g/cm^3, the strength of 1 275 MPa, the elongation of 5%, and hardness of HRC36. With the increase of sintering temperature, the density, strength and hardness increase, while the elongation decreases. The 17-4PH stainless steel has good corrosion resistance, showing an activation-passivation polarization curve. But the passivation potential range is narrow and the spot corrosion potential is low, indicating a low anti-spot corrosive properties.

New development of powder metallurgy in automotive industry

The driving force for using powder metallurgy(PM)mostly relies on its near net-shape ability and cost-performance ratio.The automotive application is a main market of PM industry,requiring parts with competitive mechanical or functional performance in a mass production scale.As the automobile technology transforms from traditional internal combustion engine vehicles to new energy vehicles,PM technology is undergoing significant changes in manufacturing and materials development.This review outlines the challenges and opportunities generated by the changes in the automotive technology for PM.Low-cost,high-performance and light-weight are critical aspects for future PM materials development.Therefore,the studies on PM lean-alloyed steel,aluminum alloys,and titanium alloy materials were reviewed.In addition,PM soft magnetic composite applied to new energy vehicles was discussed.Then new opportunities for advanced processing,such as metal injection molding(MIM)and additive manufacturing(AM),in automotive industry were stated.In general,the change in automotive industry raises sufficient development space for PM.While,emerging technologies require more preeminent PM materials.Iron-based parts are still the main PM products due to their mechanical performance and low cost.MIM will occupy the growing market of highly flexible and complex parts.AM opens a door for fast prototyping,great flexibility and customizing at low cost,driving weight and assembling reduction.

粉末装载量对W-Ni-FeMIM合金喂料粘度及力学性能的影响

对粉末装载量对ＷＮｉＦｅＭＩＭ合金喂料的粘度及力学性能的影响进行了研究，发现喂料粘度随粉末装载量的升高而增大，但不同粉末装载量喂料的应变敏感性因子基本一致，呈现基本相同的假塑性体流变行为。ＷＮｉＦｅ喂料存在一最佳粉末装载量，此时合金力学性能最好，低于或高于这个粉末装载量都使得合金力学性能降低。

烧结气氛对MIM316L不锈钢致密化和尺寸精度的影响

用注射成形方法(MIM)制备了316L不锈钢样品,并在Ar、Ar+H2、N2、N2+H2和低真空5种气氛下对样品进行了烧结,讨论了烧结气氛对合金致密化、力学性能和尺寸精度的影响.结果表明:烧结气氛的露点显著影响着合金的致密化和最终力学性能;烧结气氛中的H2可以脱去合金中的碳来影响致密化和力学性能;用注射成形获得的最终样品尺寸精度受注射、脱脂和烧结工序的影响;在采用溶剂脱脂时,3个工序对尺寸精度的影响由大至小依次为烧结、注射和脱脂.在不同气氛下,3个工序对尺寸精度的影响相对稳定.

采用氢化-脱氢(HDH)钛粉和氢化钛粉制备MIMTi-6Al-4V合金

以HDH钛粉制备MIMTi-6Al-4V合金的过程为参照,对使用氢化钛粉为原料制备P/M模压钛合金以及MIM钛合金的工艺过程进行了探索。使用HDH钛粉制备的MIMTi-6Al-4V合金抗拉强度为819MPa,拉伸样延伸率为7%;使用氢化钛粉制备的P/M模压Ti-6Al-4V合金拉伸样抗拉性能高于850MPa;使用氢化钛粉为原料制备MIMTi-6Al-4V合金,顺利实现了脱氢-脱脂过程。

MIM用金属粉末的现状及发展

介绍了金属注射成形工艺对粉末的基本要求及其选用原则,详细阐述了几种典型制粉方法的原理、特点及应用。同时根据未来MIM的发展趋势,对其所用粉末提出了新的展望。

微晶蜡对MIM多元蜡基粘结剂性能的影响

研究了微晶蜡MW的加入对PW-EVA-HDPE蜡基粘结剂、喂料的均匀性、流变特性的影响。对比实验发现MW加入不会明显改变粘结剂的粘度,加入20%MW(质量分数)的蜡基体强度提高了5倍,体积收缩率降低到6.44%,使多元蜡基粘结剂从粗大层片状(50μm^150μm)结晶细化为均匀的微细晶(5μm^8μm);一定量的MW可以改善PW-EVA-HDPE三元蜡基粘结剂的组织均匀性和热稳定性,升高注射温度,能提高粉末装载量和粉末在粘结剂中分散的均匀性,从而提高产品的成品率和尺寸精度。

热等静压及后续热处理对MIM418涡轮合金组织与性能的影响

比较了热等静压前后MIM418合金组织与致密度的变化,研究了不同淬火(水冷和空冷)、时效工艺对热等静压后固溶态MIM418合金微观组织及各种析出相的影响,利用扫描电镜、透射电镜、能谱分析等手段分析了合金中主要强化相γ'和碳化物二者的形态、大小和分布的规律。结果表明,热等静压可明显提高MIM418合金的致密度,但对显微组织影响不大,"固溶+中温时效"可以获得较好的硬化效果,主要析出强化相γ'和二次碳化物的析出受固溶冷却方式的影响较大,γ'相纳米化和二次碳化物的析出或将有益于MIM418硬度的大幅度提高。

烧结气氛对MIM316L不锈钢微观组织和性能的影响

在Ar、Ar +H2 、N2 、N2 +H2 四种气氛下对MIM 31 6L不锈钢进行了烧结 ,讨论了烧结气氛对样品C、O、N含量、烧结密度、晶粒形貌和力学性能的影响。结果表明四种气氛烧结下样品C、O、N含量可控制在许可范围内。烧结气氛的露点显著影响着合金的致密化和最终力学性能 ;N2 +H2 气氛烧结下样品的抗拉强度和延伸率分别可达到 76 5MPa和 32 % ;Ar和Ar+H2 气氛烧结下样品致密化程度高 (可达理论密度的 98% ) ,孔隙细小、圆滑、分布均匀 ,晶粒尺寸大约为 5 0 μm ;样品的力学性能如下 :极限拉伸强度 6 30MPa、屈服强度 2 80MPa、延伸率5 2 %、硬度HRB 6 9 5。

MIM石蜡基热塑性粘结剂的流变学性能和脱脂性能

研究了具有不同聚合物组元的几种石蜡基粘结剂和喂料的流变学性能及脱脂性能，比较了聚合物组元对其流变学性能、脱脂性能及产品力学性能和尺寸收缩性能的影响，结果表明。

MIM Fe 基合金的合金化强化

研究金属粉末注射成形（ＭＩＭ）铁基合金在强还原性氢气氛烧结条件下的合金化强化效果。结果表明，添加Ｃｕ、Ｎｉ、Ｍｏ等元素能取得显著的固溶强化效果，其中成分为Ｆｅ２Ｎｉ２Ｃｕ０．４５Ｍｏ的机械性能达到σｂ＝４８３ＭＰａ，σｓ＝３４０ＭＰａ，δ＝９％和ＨＲＢ８３。

MIM支持块的充模流动计算机模拟

以流体力学和热力学理论为基础 ,建立了充模流动过程的控制方程、初始条件和边界条件 ,并以支持块的充模流动为例 ,采用大型通用有限元软件ANSYS进行了计算机模拟 ,着重研究了浇口位置和浇口尺寸大小对压力场 ,温度场的影响 ,同时结合实验分析了转角处缺陷产生的机理。模拟结果表明 :当采用尺寸大小为 4mm的中间浇口进行注射时 ,可以得到良好的支持块预成形坯 ,与实验结果一致。

金属注射成型(MIM)综合脱脂炉的结构设计特点

介绍了金属注射成型(M IM)综合脱脂炉的结构设计特点,该设计可同时满足包括溶剂、催化、冷凝蒸汽、虹吸脱脂在内的脱脂工艺要求。

MIM蜡基粘结剂蜡含量对成形性的影响

采用不同石蜡含量的多聚合物组元粘结剂,研究石蜡含量对喂料粘度、生坯密度均匀性、生坯强度的影响。石蜡含量提高改善了喂料的均匀流变性能,但降低了生坯的抗破坯能力。研究结果为蜡基粘结剂的合理选择提供了依据。

MIM零件烧结过程中收缩和变形的数值模拟

为描述金属粉末注射成形坯件在烧结过程中的收缩和变形行为,基于连续介质力学原理建立了符合粘塑性本构关系的宏观烧结模型。该模型通过有限元软件Abaqus的用户子程序实现,进行烧结过程的数值模拟。分析了由于坯件重力、非均匀初始密度分布以及坯件支承体之间的摩擦力等因素而引起的非均匀收缩和变形。通过与试验结果的比较,验证了烧结模型和数值方法的正确性。

水溶性MIM粘结剂的制备及性能表征

以PEG和POM为主体组分配方制备了一种用于金属粉末注射成型用的水溶性粘结剂.通过扫描电镜分析、差示扫描量分析仪、热重分析仪及热性能测试、脱脂率实验等对制备的粘结剂体系进行分析表征.结果表明:该粘结剂体系组分之间有很好的相容性,和金属粉末的混合性良好;该种粘结剂在水中脱脂速度快,脱脂率高,在75℃水中4h内的脱脂率43.06%;粘结剂体系具备良好的热分解性能,添加剂的加入使得热分解温度降低,有利于烧结的进行.