Study On Hollow Cathode Sintering And Alloying Process Of Ferrous P/M Materials

The sintering of powder metallurgy material and product is an important way of preparation and processing of new material currently. The sintering is a key segment of deciding the quality of powder metallurgy product. Because preparation and processing of new material requires sintering method strictly, corresponding new technology appears continously, such as Hot Isostatic Sintering, Laser Sintering, Spark Plasma Sintering, but these methods have their applying area and cannot meet the demand of developing of new material. Researching and designing new sintering method is still an important topic of powder metallurgy field. Hollow Cathode Sintering process use Hollow Cathode Discharging effect as new sintering facility, implement high-speed sintering of metal. Introducing metallic cementation at the same time, thus the surface of material will form alloying layer, it will improve the surface property of material.Hollow Cathode Sintering of iron powder can be divided into three steps: bonding step, sintering neck-growth step, pore-reducing step. In the sintering process, the pore shrinks gradually, it approaches to sphere finally, the grain will appear recrystalization and grain-growth. In the process of sintering, the density of sample will increase as the sintering temperature increases, the body of sintering compacts obviously. Hollow Cathode Sintering of iron powder have advantages as follows: providing heat energy without other heating components.After nickelizing it will obtain nickel layer consist of diffusion layer. Thus the work will have high erosion resistance and anti-high temperature oxidation. We will study the influencing factor of layer thickness and density, The results show that, as the sintering temperature increases, the whole layer thickness increases rapidly, The layer thickness will increase as the keeping time extends. The tissue of nickel layer is diffusion layer, The distributing characteristic of Ni concentration is decreased gradually from the layer surface to the body, but also the concentration of Ni atom is slow. As the formation of diffusion layer, the process is controlled by the extension growth and inward diffusion of Ni content. The content of Ni atoms from surface deposition is larger than those from entering body, Ni atom forms alloy in the surface deposition.At the same time, after tungstenizing it will obtain compact matrix tissue and tungsten layer, thus it will intensify wear property and red-hardness of the surface. The results show that the thickness of tungsten layer will increase as the sintering temperature heightens and the keeping time extends; By the analysis of tungsten layer microstructure, we can ontain: In different conditions, the microstructure is the same, it occurs the transformation fromγphace toαphase, the tissue of layer is columner alloyα, and there have obvious interface between tungsten layer and body, the content of tungsten in the layer or in the body of surface is low, and the concentration of tungsten falls from the surface to body, The surface of sample forms alloy Fe7W6.