Characterisation of sintering of alumina matrix–stainless steel dispersion composite and interaction between chromium,carbon and alumina during powder metallurgy process

Abstract

This paper aims to study the sintering of 316L stainless steel and alumina composites. Compositions range from 0 to 100 vol.-% steel, and the experimental procedures involve density and microstructure analysis of the samples, as well as dilatometric measurements. In this study, it is shown that reducing atmosphere debinding can lead to carbon residues. These have a negative effect on alumina densification by delaying the sintering onset. For metal–ceramic composites, densification is modified by a complex interaction involving carbon (which lowers alumina density), chromium oxide (which is documented in literature to diminish alumina densification) and stainless steel phase. Chromium carbide formation is possible for some experimental conditions (1–30% stainless steel and hydrogenated argon debinding); this mechanism, locking both carbon and chromium outside alumina phase, leads to higher sintered densities.     

Finite element investigation of backbone binder removal from MIM copper compact

Abstract

Finite element (FE) model based on kinetic analysis was developed to describe the thermal debinding process of previously solvent debinded metal injection moulded (MIM) copper compacts. Thermophysical properties (specific heat, density, thermal diffusivity and thermal conductivity as a function of temperature) of MIM copper compact were measured using differential scanning calorimeter, laser flash analyser, thermogravimetry analyser and pushrod dilatometer. The proposed model is solved numerically to study binder removal and binder distribution during thermal debinding. The investigations included the analysis of residual (backbone) binder content for cylindrical MIM copper compacts at different temperatures and positions. The FE calculations are strongly based on measured thermophysical data and kinetic analysis of copper system. The FE simulated and experimental results were compared to validate the underlying FE model based on FE temperature field calculations. Drawing the real furnace temperature conditions in finite calculation can result in obtaining more accurate data.     

Hot micro-embossing: effect of pressure on 316L metal parts

Abstract

The use of replicative processes has become strategic and critical in industry to produce precise, microscopically detailed metallic parts and devices via low cost manufacturing routes. Metal powder hot embossing is an emerging process that brings some advantages associated with the reduction of production costs relative to powder injection moulding (PIM). The technology involves four distinct steps: preparation of the selected feedstock material (powder and binder); hot embossing; debinding; and sintering. The effect of continuous pressure during the hot embossing step as a means of replicating microdetails in 316L stainless steel parts is examined. Dimensional accuracy, microstructure and mechanical properties of the parts produced were evaluated. For the configuration tested, the most promising results were achieved when processing at 180°C for 30 min at a pressure of 14 MPa.     

In situ dimensional change,mass loss and mechanisms for solvent debinding of powder injection moulded components

Abstract

Dimensional change during solvent debinding is linked to defects such as cracking and slumping in powder injection moulded components. Owing to the delicate condition of the compact during debinding, considerable difficulty exists in determining the magnitude and cause of swelling or shrinkage. Previous studies of this dimensional change have used measurement techniques involving contact or force on the sample, which may alter the behaviour. This study observes in situ dimensional change during solvent debinding using a non-contact laser dilatometer. Dimensional change was investigated for iron and stainless steel powder injection moulded bars with wax-polymer binders. The effects of solvent temperature, paraffin wax content, paraffin wax density, particle size and solids loading were analysed. Comparisons between the dimensional change and mass loss observations during solvent debinding suggest a relationship between the two phenomena based on soluble polymer swelling.     

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 residual carbon on the sintering process of M2 high speed steel parts obtained by a modified metal injection molding process

In this article, we present the evolution of the microstructure during sintering of M2 high speed steel (HSS) parts obtained by a modified powder injection molding (PIM) process, which uses a new binder system based on a thermosetting resin. The most important characteristics of this process is that molding is carried out at room temperature by pouring the slurry (resin and tool steel previously mixed) directly into the mold. The mold is then heated to the curing temperature of the resin. The best mixture of polymer and steel powders was 60 pct volume of metal powder. The resin was removed by thermal debinding. The sintering process was carried out under vacuum atmosphere. We tested different debinding temperatures in order to retain residual carbon in the samples coming from the thermal degradation of the polymer. The best results were obtained at low debinding temperature (300 °C). In this case, residual carbon had a beneficial effect, extending the sintering temperature range by 100 deg, making it possible to reach very high density at temperatures as low as 1100 °C. The mechanism of this densification seems to be via supersolidus liquid phase (SPLS). The microstructural study of sintered parts revealed a homogeneous distribution of carbides that change their morphology with increasing temperature. Besides spherical M₆C carbides, which appear in all the temperature ranges studied, a new rodlike M₂C carbide appears.     

EURO PM2009 in cool Copenhagen

Abstract

The effect of additions of silicon powder on the sintering behaviour and microstructure of compacted 304L stainless powder has been studied. The shrinkage ratio increases substantially with silicon content. Silicon profoundly activates the sintering process through the formation of a eutectic and/or δ ferrite, which is pseudoperitectically formed during sintering. The sintering behaviour is closely related to the microstructures, which depend upon the amount of silicon addition. Ostwald ripening is encountered in the liquid phase sintered specimens (Si≤3 wt-%). The solid phase sintered materials (Si≥ wt-%) containing δ ferrite densify more rapidly than the liquid phase sintered ones. The densification kinetics are governed by the wetting characteristics of the eutectic liquid and the formation of ferrite. As a result of the silicon addition, the austenitic stainless steel powder aggregates are sintered into duplex stainless steels with austenite-ferrite structures. PM/0395     

Dilatometric analysis of thermal debinding of injection moulded iron compacts

Abstract

The less than desired tolerance control of powder injection moulded compacts is a result of inconsistent dimensional changes in the compacts accumulated during moulding, debinding, and sintering. This study investigated the in situ length changes and their causes during thermal debinding on compacts which have been solvent debound. The dilatometric analysis showed that the specimen shrank in the early stage between 250 and 370°C, not because of sintering, but through the loss of N, C, and O in the carbonyl iron powder. At temperatures between 370 and 450°C, the specimen expanded owing to the carburisation of the iron powder. The length change was also influenced by the heating rate, debinding atmosphere, and the amount of the backbone binder. These dilatometric results are helpful in establishing the guidelines in designing binder compositions and debinding schedules.     

国外注射成形不锈钢研究的进展

本文以 31 6L和 1 7 4PH不锈钢为主 ,从不锈钢粉末制备、粘结剂与脱脂技术、烧结技术及性能等方面 ,综述了国外注射成形不锈钢技术研究的进展 ,并列出一些主要的应用领域     

MIM零件的先进热加工工艺及设备

本文介绍了金属粉末注射成形 (MIM)零件的先进热加工工艺及设备。由于MIM Mas ter系列设备具有连续脱粘 高温烧结及快速冷却功能 ,可在大规模生产时加强工艺参数的控制 ,改善产品质量。最后把高温烧结和快速冷却组成一个连续过程 ,能实现MIM零件烧成品的硬化。快速冷却的独特优点是在分解氨气氛中烧结 316L不锈钢可提高其密度 ,并可以采用可靠而价廉的气氛以降低成本     

3D FE Analysis of Thermal Behavior of Billet in Rod and Wire Hot Continuous Rolling Process

 An FE model was developed to study thermal behavior during the rod and wire hot continuous rolling process. The FE code MSCMarc was used in the simulation using implicit static arithmetic. The whole rolling process of 30 passes was separated and simulated with several continuous 3D elastic plastic FE models. A rigid pushing body and a data transfer technique were introduced into this model. The on line experiments were conducted on 304 stainless steel and GCr15 steel hot continuous rolling process to prove the results of simulation by implicit static FEM. The results show that the temperature results of finite element simulations are in good agreement with experiments, which indicate that the FE model developed in this study is effective and efficient.     

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.     

Influence of injection moulding and sintering parameters on properties of 316L MIM compact

Abstract

This study elucidates the effects of key injection moulding and sintering factors on the dimensions and mechanical properties of 316L stainless steel metal injection moulded compact. Sintered parts of optimal quality can be produced by properly setting the process parameters. Taguchi method and principal component analysis are performed initially to elucidate and optimise the key control factors that affect the qualities of metal injection moulded compact. Next, a feasible process window is tested by observing the powder and binder distribution of green parts, for various control factors of injection moulding. Experimental findings show that, first, a proper injection speed facilitates mould filling during injection moulding and so improving the quality of sintered parts; second, temperature critically determines the rate of dimensional shrinkage, density and hardness of sintered parts; Third, optimal parameters setting can efficiently improve the quality of 316L metal injection moulded compact.     

Sintering transformations in mixtures of austenitic and ferritic stainless steel powders

Abstract

The microstructural transformations and the dimensional evolution of green specimens obtained by pressing mixtures of austenitic and ferritic stainless steel powders have been investigated by sintering at 1120 and 1240°C. Dilatometry experiments show that the linear shrinkage is influenced by the amount of ferritic powder. Moreover, during sintering Ni diffuses into the ferritic grains causing austenite destabilisation and the formation of a mixed constituent, whose constitution has been investigated by means of EDXS and interpreted on the basis of the Schaeffler diagram. Sigma phase also forms during sintering of the duplex mixtures.     

High density sintering of duplex stainless steels

Abstract

Duplex stainless steels prepared from mixes of elemental powders with martensitic 410L steel have been shown to possess stable dual phase microstructures. Following heat treatment, the steels possess good mechanical properties. The addition of boron as a sintering aid reduces compressibility but promotes densification through transient liquid phase sintering; its effect on corrosion resistance is particularly favourable.     

不锈钢/碳钢包层钢筋轧制模拟分析与试验研究

 研究了不锈钢/碳钢包层钢筋轧制过程中,轧件尺寸变化情况以及金属的流动规律。应用MSC.Marc对不锈钢/碳钢包层钢筋轧制过程进行了有限元模拟。基于软件二次开发,判断两金属的结合状态。通过和均质碳钢钢筋轧制模拟结果进行对比,并经包层钢筋轧制试验验证,结果表明：轧制过程中,不锈钢包层钢筋芯部的轴向延伸阻力大于均质碳钢钢筋,造成包层钢筋的宽展大于均质碳钢钢筋,因此,不能应用轧制均质碳钢钢筋的孔型轧制包层钢筋。包层钢筋的模拟结果与试验比较吻合,证明孔设计合理且有限元模型可靠。