Injection moulding of 316L stainless steels reinforced with nanosize alumina particles

Abstract

This study aims to compare the effect of Al₂O₃ nanoparticle additions on the densification and mechanical properties of the injection moulded 316L stainless steels. The 316L stainless steel and Al₂O₃ nanoparticles were dry mixed and moulded using a wax based binder. The critical powder loading for injection moulding were 60 vol.-% for all samples. Debinding process was performed in solvent using thermal method. After the debinding process, the samples were sintered at 1405°C for 60 and 120 min under vacuum. Metallographic examination was conducted to determine the extend of densification and the corresponding microstructural changes. The sintered samples were characterised by measuring tensile strength, hardness and wear behaviour. Wear loss was determined for all the samples after wear testing. All the powders, fracture surfaces of moulded and sintered samples were examined using scanning electron microscope. The sintered density of straight as well as Al₂O₃ nanoparticles reinforced injection moulded 316L stainless steels increases with the increase in sintering time. The additions of Al₂O₃ nanoparticles improve the hardness and wear resistance with the increase of sintering time.     

MlM316L不锈钢致密化和尺寸精度的研究

在Ar,Ar+H_2,N_2,N_2+H_2和低真空5种气氛下对MIM316L不锈钢进行了烧结,讨论了烧结气氛对合金致密化和力学性能的影响;得出烧结气氛的露点显著影响合金的致密化和最终力学性能;烧结气氛中的H_2可以脱去合金中的碳来影响致密化和力学性能;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。     

Effect of additives on sintering response of titanium by powder injection moulding

Abstract

Powder injection moulding is a maturing technology that has proven most useful for the production of complex metallic and ceramic components of modest sizes. Considering the inevitable demand for cost effectiveness in automotive applications, components manufactured from low cost sponge titanium (Ti) powder currently reflect the most advantageous economics among the available Ti powders. This paper describes the net shape fabrication of Ti components and considers the role of iron and zirconium powder additions. Sintering cycle optimisation relied on differential scanning calorimetry to identify a cycle in the 1275–1300°C range for 1–2 h. The sintered material was characterised using tensile and hardness testing and microscopic examinations. The influence of test conditions on densification, microstructure and mechanical properties was analysed.     

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 316L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765 MPa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50μm;样品的力学性能如下极限拉伸强度630 MPa、屈服强度280 MPa、延伸率52 %、硬度HRB 69.5.     

Sintering parameters and mechanical properties of injection moulded aluminium powder

Abstract

This paper describes the microstructural and mechanical properties of injection moulded aluminium powder. Gas atomised aluminium powder was injection moulded with wax based binder. The critical powder loading for injection moulding was 62·5 vol.-% for feedstock. Binder debinding was performed in solvent and thermal method. After debinding, the samples were sintered at different temperatures and times in high purity N₂. Metallographic studies were conducted to determine the extent of densification and the corresponding microstructural changes. The results show that gas atomised aluminium powder could be sintered to a maximum 96·2% of theoretical density. Maximum density, tensile strength and hardness were obtained when sintered at 650°C for 60 min.     

316L、317L的MIM注射成形生坯件溶剂脱脂工艺研究

介绍了316L、317L两种不锈钢MIM生坯溶剂脱脂过程中溶剂种类、溶剂温度、工件厚度、钢粉的粒度及形貌对溶剂脱脂过程的影响。结果表明：选择正己烷作溶剂，控制溶剂温度37℃可以避免溶剂脱脂过程中工件开裂、鼓泡问题，而且能减少对环境的污染，给操作者提供更好的劳动条件；溶剂脱脂早期大粒度球形钢粉的生坯要比小粒度不规则形状钢粉的生坯脱脂速度快，但后期小粒度不规则形状钢粉的生坯脱脂较大粒度球形钢粉的生坯速度快。     

Metal injection moulding (MIM) as an alternative fabrication process for the production of TWIP steel

Twinning Induced Plasticity (TWIP) steels are high manganese austenitic steels that have caused growing interest over the last decade due to their unique combination of strength and elongation. Nevertheless, the problems presented during their current fabrication process (continuous casting) complicate their production and commercialisation. Powder metallurgy may be an attractive alternative route of solving these problems in certain components. In this work, Metal Injection Moulding (MIM) is explored as an alternative fabrication method for TWIP steels, having the additional benefit of reaching a near-theoretical densification. The feedstock of this study is composed of a metallic prealloyed Fe–Mn–C–Al–Si powder and a binder system based on wax-HDPE. The feedstock was optimised by examining different metallic loads. A suitable powder–binder ratio was determined based on mixing torque and melt flow index measurements. It was optimised a two-stage debinding process and a sintering process in an argon atmosphere to obtain the correct microstructure.     

烧结工艺对316L不锈钢组织与性能的影响

通过研究烧结气氛和烧结温度对冷等静压态316L不锈钢组织和力学性能的影响,探究了烧结的致密化过程,并初步分析了挤压之后不锈钢的组织与性能。发现真空条件下获得的力学性能均比Ar气氛下烧结的好;在N2气氛烧结的不锈钢抗拉强度为803.5 MPa,屈服强度为407.2 MPa,但是断后延伸率仅为33.7%。在真空气氛下进行烧结,随温度的升高,孔隙率下降、孔隙尺寸减小并发生球化;通过对比烧结温度的影响,得出在1 380℃进行烧结获得的力学性能最好,抗拉强度为578.4 MPa,断后伸长率为52.0%,并且晶粒比较细小。经过挤压处理,不锈钢晶粒进一步细化,抗拉强度为675.6 MPa,屈服强度为305.4 MPa,断后伸长率为45.6%。     

氮对316L型不锈钢等离子弧焊接性能的影响

氮作为一种强奥氏体化元素,在不降低韧性的前提下可以提高材料强度和抗腐蚀性能。为了研究氮含量对316L型不锈钢焊接性能的影响,采用两种不同氮含量的316L型不锈钢进行不填丝穿孔等离子弧焊接。通过力学、抗晶间腐蚀等性能的对比,结合金相组织观察,可以看出奥氏体不锈钢中氮元素含量的增加能够提高焊接接头的抗拉强度,但却促进了热影响区晶粒的粗化,导致热影响区的低温冲击性能降低。     

Multiphysic coupling and full cycle simulation of microwave sintering applied to a ceramic compact obtained by ceramic injection moulding

Microwave sintering represents the coupling of multiple physical phenomena. It involves the distribution of electromagnetic fields, heat generation by electromagnetic effects, heat conduction in the material, and evolution of the densification in the sintered components. This paper describes the mathematical models and the numerical methods used to simulate the complex sintering process. Simulation results are provided for the prediction of shrinkage and evolution of the relative density of the sintered materials. A full cycle simulation of the microwave sintering process have been realized on the COMSOL Multiphysics finite element software platform. This work provides an important approach to studying the process of microwave sintering. The simulation results for sintering submicron zirconia powders are compared with experimental results in terms of the relative densities of the sintered material.     

Metal injection moulding of nickel-based superalloy CM247LC*

Metal injection moulding (MIM) is a promising new production technology for small- to medium-sized parts with high complexity for high-temperature applications like aero engines or turbochargers. This study concerns the feasibility of manufacturing parts from nickel-based superalloy CM247LC via MIM. CM247LC poses a serious challenge for MIM processing. Because of its high aluminium content, the strength potential is very high, but the sintering capability is severely restricted. Differential scanning calorimetry and dilatometry measurements as well as ThermoCalc simulations are used to optimise the sintering step of the MIM process route. Carbon, nitrogen and oxygen contents of the powder and the as-sintered specimens are measured to evaluate the pick-up of impurities during processing. The microstructure of the as-sintered specimens is characterised with respect to residual porosity, grain size, carbide content and γ′ precipitation size and morphology. Ways to further improve the microstructure and strength will be discussed.     

Enhanced sintering and mechanical properties of 316L stainless steel with silicon additions as sintering aid

Abstract

Compaction, effect of ball milling, vaccum sintering, microstructures, volume shrinkage, interconnected porosity, thermal reactions and mechanical properties of 316L stainless steel with and without additions of elemental silicon have been investigated. It was found that the silicon addition enhanced the sintering process by providing a series of liquid phase reactions with the base powder which took place at temperatures below their melting points and the normal solidus range for stainless steels. Differential thermal analysis confirmed formation of liquid phases at three different temperatures which are believed to be responsible for the enhanced sintering process.The first two appeared at ~1060 and 1155°C by two exothermic peaks and the third one at ~1190°C by an endothermic peak. The ball milling operation provided higher green and sintered densities resulting in better mechanical properties due to less agglomorations with finer and much more uniform particle size distribution. Sintered densities of up to 7·44 g cm^-3 with tensile strength of 482 MPa, hardness value of 153 HV10 and 15% elongation were obtained with ball milled plus 3 wt-%Si addition. Low levels of interconnected porosities (~4%) were recorded within the temperature range 1250-1300°C suggesting the possibility of good corrosion resistance.

The sintered microstructures consisted of ferrite and austenite (duplex structure), complex silicide and eutectic phases within grains and at grain boundaries, pools of liquid (rich in Si) and some medium and small pores preventing full density to be achieved despite the liquid phase formation.     

热处理对316L不锈钢组织和性能的影响

通过试验研究了不同热处理工艺对316L不锈钢组织和性能的影响.试验结果表明,1 000℃固溶处理30min的硬度最大(77.8 HRB)、晶粒最细.若提高固溶处理温度,可以改善钢的抗腐蚀性,但温度过高,会降低钢的硬度.与固溶处理相比,由于发生时效硬化,固溶处理后进行时效处理的硬度更高、显微组织更好.     

Mechanical properties of metal injection moulded 316L stainless steel using both prealloy and master alloy techniques

Abstract

Stainless steel 316L MIM components can be made from either prealloyed powders or from master alloys blended with carbonyl iron powder. In this study these two techniques were compared using prealloyed and master alloyed gas atomised powders of ? 16 μm and ? 22 μm sizes. Four different compounds were prepared, characterised and injection moulded into tensile bars. The bars were compared for green strength, green defects, sintered strength and microstructure. The green components are stronger when carbonyl iron powder is used with the gas atomised master alloy. This material also seems to be less susceptible to moulding defects. The sintering strength of the material produced using the pre-alloyed powder was higher than the master alloyed prepared material. Little difference in mechanical properties existed between the materials fabricated from gas atomised prealloyed ? 16 μm and the ? 22 μm powders. Also, the viscosity of the mixtures was higher for the ? 16 μm material and the master alloy mixtures than for the –22 μm gas atomised prealloyed powders.     

Powder extrusion moulding of 430L stainless steel thin tubes for porous metal supported SOFCs

Abstract

Thin and thick walled tubes made of 430L stainless steel for porous metal supported solid oxide fuel cells (SOFCs) were prepared by powder extrusion moulding (PEM). A gas atomised metal powder and a binder composed by 50?vol.‐% high density polyethylene and 50?vol.‐% paraffin wax were chosen. The most suitable powder loading for feedstock (68?vol.‐%) was determined by means of torque experiments and rheological measurements. Mixing temperature was selected taking into account the results from differential scanning calorimetry. The extrusion of tubes was carried out in a single screw extruder and two kinds of tubes with two different wall thicknesses were obtained. In order to investigate the homogeneity of feedstock, microstructure of green tubes was evaluated by SEM. Thermal debinding was performed on the basis of thermogravimetric analysis results. After sintering, tubes with good dimensional stability and without defects were obtained. Different wall thicknesses extruded were 150 and 500?μm.     

Characterisation of 316L powder injection moulding feedstock for purpose of numerical simulation of PIM process

Abstract

Viscosity, specific heat and thermal conductivity of the standard feedstock of 316L stainless steel have been measured under the typical conditions of a real powder injection moulding (PIM) process. The viscosity was measured in a wide range of shear rates at four different temperatures. The experimental viscosity data were fitted into the Carreau-Yasuda model. Both specific heat and thermal conductivity were measured in the temperature range that overlaps the recommended processing range for the studied feedstock. It has been shown that at high cooling rates the transition temperature of the binder material is shifted towards lower temperatures. Tabulated values of thermal conductivity and specific heat for the studied feedstock are presented. The obtained data can be used for numerical simulation of the powder injection moulding process.     

316L不锈钢/Y-PSZ复合材料的制备与性能

采用粉末冶金方法制备了316L不锈钢/Y-PSZ复合材料,研究了316L不锈钢含量与粉末粒度对复合材料的显微组织、烧结收缩率、密度及硬度的影响.结果表明:随着316L含量的增加,复合材料的密度增高,相对密度和烧结收缩率逐渐降低,试样的HRC硬度值下降;在316L含量一定的情况下,随着316L颗粒尺寸的增大,复合材料的密度略有降低,相对密度和线收缩率逐渐减小,试样的HRC硬度值下降.在本文的研究条件下,所制备复合材料的相对密度值在92.5%~95.5%之间.     

316L不锈钢表面沉积CrCN薄膜的结构及性能研究

利用多弧离子镀技术在316L不锈钢和单晶硅上沉积CrCN薄膜,通过X射线衍射仪(XRD)、扫描电镜(SEM)、X射线光电子能谱仪(XPS)、纳米压痕仪、273A电化学工作站和多功能摩擦磨损试验机等对316L不锈钢及CrCN薄膜的微观结构、力学性能、耐腐蚀性能和摩擦学性能进行表征.结果表明:在316L不锈钢上沉积CrCN薄膜后,硬度从4 GPa提高到22 GPa,H/E和H3/E2分别从0.022和0.002 GPa提高到0.071和0.11 GPa;阳极腐蚀电位从-0.21 V上升到-0.19 V;在大气,去离子水,海水环境下的摩擦系数及磨损率均显著降低,表现出较优异的综合性能.     

添加金属粉末对粉末冶金316L不锈钢性能的影响

研究了分别添加20％（质量分数）铜粉、锡粉，铝粉对粉末冶金3161，不锈钢性能的影响。在烧结温度为1100℃、烧结气氛为分解氨的条件下，对烧结材料的硬度、密度和显微组织进行了检测和分析。结果表明：添加20％铝粉可显著提高不锈钢粉末的压制性，但铝粉会与不锈钢基体发生强烈的化学反应，生成Fe2Al，恶化材料的性能；添加20％锡粉可显著提高材料的硬度；添加20％铜粉对材料的硬度影响不大。添加大量低熔点金属粉末的液相烧结不能显著提高材料的密度。