Jan Kazior

Effect of atmosphere on sintering of Alumix 431D powder

Abstract Dilatometry and differential scanning calorimetry analyses were used to study the sintering response of Al based powder mixture produced by ECKA Granules, designated as Alumix 431D. Sintering was carried out in atmospheres of pure nitrogen, nitrogen–hydrogen mixture (95∶5 by volume) and argon. The atmosphere influences the amount of shrinkage but not the sintering mechanisms. These are similar for all gases; typical liquid phase sintering mechanisms seem to be mainly responsible for the sintering behaviour. As expected, however, nitrogen is the most effective sintering atmosphere in terms of densification. Metallographic examinations are in accord with the results of thermal analyses.

Dilatometric study of solid state sintering of austenitic stainless steel

Abstract Examination of the dimensional behaviour of AISI 316L austenitic stainless steel during sintering in high purity hydrogen was carried out using dilatometric method. Influence of the heating rate on dimensional changes and sintered microstructure was established. It was shown that the heating rate influences both the kinetic of shrinkage and microstructure but not the final density of sintered compacts.

Investigation of liquid-phase sintering by image analysis

Abstract The liquid-phase sintering of austenitic stainless steel alloyed with boron was studied by means of image analysis. By evaluating fractional porosity, the amount of liquid constituent, grain size, and pore morphology, the effect of boron content and sintering time on the sintering process was determined and discussed on the basis of the classic theory of liquid-phase sintering. Image analysis proves to be a powerful tool for optimizing the liquidphase sintering process.

Thermochemical treatment of Fe–Cr–Mo alloys

Abstract Thermochemical treatment in different atmospheres containing nitrogen, sulfur and oxygen was applied to the sintered prealloyed powder Astaloy CrM containing 3 wt.% Cr and 0.5 wt.% Mo. The base material was modified by boron and carbon addition. In this paper, special attention was paid to explaining the influence of the microstructure of the base material on the formation of a compound layer and the wear resistance of surface-treated sintered components. A bainitic–martensitic microstructure was obtained after sintering. Depending on the nitriding atmosphere, nitriding (N), oxynitriding (NO), sulfonitriding (NS) or oxysulfonitriding (NSO), the compound layer of the surface-treated specimen has a different constitution and compactness. Wear resistance investigations under dry sliding conditions show that sulfonitriding, due to the presence of iron sulfide, which possesses excellent friction properties against steel, particularly improves the wear resistance of the sintered Astaloy CrM.

Surface self-densification in boron alloyed austenitic stainless steel and its effect on corrosion and impact resistance

Abstract A boron alloyed AISI 316L, sintered in pure hydrogen at 1250°C, was investigated to study the effect of the microstructure, with particular reference to the near full dense and boride free surface layers, on corrosion resistance and impact properties. The near full dense and homogeneous austenitic surface layer results from the flow of the liquid towards the bulk of the specimens during sintering. It significantly improves the corrosion resistance, while impact properties are strongly influenced by the bulk microstructure, where the boride network creates favourable conditions for both nucleation and propagation of crack.

Sinter-Bonding of Iron Based Compacts Containing P and Cu

The sinter-bonding behavior of iron based powder mixtures was investigated. To produce the green compacts to be joined the following powders based on Höganäs AB grade NC 100.24 plain iron powder were used: NC 100.24 as delivered, PNC 30, PNC 60 and NC 100.24 + 4%Cu powder mixtures. Dimensional behaviour of all those materials during the sintering cycle was monitored by dilatometry. Simple ring shaped specimens as the outer parts and cylindrical as the inner parts were pressed. The influence of parts’ composition on joining strength was established. Diffusion of alloying elements: copper and phosphorous, across the bonding surface was controlled by metallography, SEM and microanalysis.

Liquid Phase Sintering of a Boron Alloyed Austenitic Stainless Steel

It is well known that PM stainless steels have lower corrosion resistance than the corresponding wrought steels, since they are affected by the presence of the open porosity. A way to obtain a surface densification is the addition of a small quantity of boron (from 0,3 to 0,5%wt.) to the stainless steel. The presence of boron produces a liquid phase phenomenon that results in a final microstructure consisting of a boron-rich phase network surrounding the stainless steels grains. Close to the surface, a boron-free layer was observed in which pores are very few, closed and round. This leads to an improvement in the steel corrosion resistance.

Reaction sintering of Fe-Al-Si alloys

The present study concerns the production of multiphase alloys of the Fe-Al-Si system using a powder metallurgical approach. Several compositions have been considered based on α-Fe, α′-FeAl; and α″-Fe3Al intermetallic phases. Elemental powder mixtures were compacted and sintered in a dilatometer. In this way, the dimensional changes involved with thermally induced transformations could be followed during continuous heating runs up to the sintering temperature. The effect of heating rate has been considered. The characterization of the final products was based mainly on x-ray diffraction (XRD) analyses, particularly as concerns the quantification of the crystalline phases present in the final products. Grain and porosity morphologies were characterized by scanning electron microscopy (SEM). In this way, clear indications of the reaction and densification processes occurring during the sintering treatments were obtained.

Microstructure Evolution during Sintering of Aluminium in Nitrogen

High purity aluminium powder was sintered in a dilatometer in flowing high purity nitrogen. The distinct shrinkage segments observed on the dilatometry curves were the basis of experiments consisting of interrupted sintering. In this way compacts with microstructure frozen at different steps of sintering cycle were produced. Optical microstructure examinations and LECO analysis of nitrogen content showed the development of aluminium nitriding. Additionally, X-ray diffraction was used to examine phases appearing in the system investigated. Microstructure analysis of structural components revealed evidence that isothermal sintering proceeds in the presence of a liquid phase, despite taking place below the melting point of aluminium. It seems that aluminium nitrogen interactions are responsible for the appearance of this phase, which is accompanied by extensive shrinkage.

Properties of Precipitation Hardening 17-4 PH Stainless Steel Manufactured by Powder Metallurgy Technology

Alloys from austenitic and ferritic stainless steel found to be satisfactory for a great many applications. However, for applications that require higher levels of strength and hardness from the martensitic grades are frequently specified. Martensitic stainless steels offer significantly higher strengths but have to low ductility. For this reason for application where high levels of strength and a moderate ductility is required, the precipitation strengthened stainless steels are often considered. One of the most popular alloy of this kind of stainless steel is 17-4 PH. The aim of the present paper was to examined the influence the process parameters in conventional powder metallurgy processing on the mechanical properties of the 17-4 PH alloy in both as-sintered and heat treated conditions. In was found that temperature of aged is a very sensitive parameter for obtained high strength and acceptable ductility.