Preparation And Properties Of WC/NbC Particles Reinforced High Chromium Iron-based Pm Materials

High temperature, high speed and wear conditions require materials with good properties. For ordinary metal materials, it has been difficult to meet the requirements of performance under this environment, and high performance powder metallurgy materials gradually become one of the research focuses. In order to develop high performance iron-based powder metallurgy material, on the basis of early researches, in this paper, hot-press technology was used to sinter WC or Nb C reinforced nanocrystalline Fe-10Cr-1Cu-1Ni-1Mo-2C powders, and the microstructure, reinforcements, mechanical properties and wear resistance of sintered iron-based alloys were studied.The mix powders were pretreated by high energy ball milling technology, and nanocrystalline composite powders containing reinforced phases were obtained, and the influences of milling time and reinforcement content on milled powders were studied. Then, the nanocrystalline composite powder containing WC were sintered at 900℃~1100℃ by hot-press, and WC particle reinforced Fe–10Cr–1Cu–1Ni–1Mo–2C alloys were obtained. After sintering, the microstructure of alloys were mainly composed of the Cr-rich ferrite, WC, Fe3 C and M7C3(M=Fe, Cr, Mo). Comparing the microstructure of samples sintered in different temperatures, the porosity of the sintered alloy was obvious only at 900℃, and the microstructure of specimen were dense and even tiny when sintered at 1000℃ and 1050℃, while grain growth phenomenon was found in the microstructure of alloy sintered in 1100℃. The extractions of sintered alloy were of small size(< 1 μm), which were mainly composed of M7C3, WC, Fe3 C and Cr2O3 phases, the size of in-situ M7C3 were 200~500 nm, evenly distributed in the matrix and had a good interface environment with the matrix. When sintering temperature raised from 900℃ to 950℃, the porosity of sintered sample sharply reduced, the density and hardness increased significantly. As sintering temperature continue to rise, the density, hardness of the sample increase gradually, but sintering density and hardness of the alloy declined when sintered at 1100℃. In addition, the compressive strength of sintered alloy increased as the increase of sintering temperature.Based on the above research, the preparation Nb C particle reinforced Fe–10Cr–1Cu–1Ni–1Mo–2C alloy was conducted by hot-press. Microstructures and mechanical properties were analyzed, and the type, size and distribution of reinforcements of the high chromium iron-based powder metallurgy material were further studied. The microstructures were mainly composed of the Cr-rich ferrite, Nb C, Fe3 C and M7C3. The extractions of sintered alloy were of small size, which were mainly composed of M7C3, Nb C, Fe3 C and Cr2O3 phases. Within all the reinforcements, the size of in-situ M7C3 was the largest, which reached more than 500 nm, and the interface between ferrite matrix and the in-situ M7C3 was clean. With the increase of sintering temperature, the density of sintered specimen increased, when the sintering temperature was above 1000℃, all of the specimens were dense, and density of sample sintered at 1100℃ was the highest(99.7% of the theoretical density). The compressive strength of sintered alloy increases with the raising of sintering temperature, and the compressive strengths of samples sintered above 1000℃ were obove 2100 MPa.In view of the practical application environment of high performance iron-based powder metallurgy materials, high temperature tensile property and friction wear performance test were conducted. High temperature tensile properties of various temperatures and different WC content were studied, and the influence of sintering temperature and the content of reinforcement phase on friction wear performance were also investigated. After high energy ball milling and hot-press, the sintered specimen alloys with 0wt.% WC, 5wt.% WC and 8wt.% WC had good tensile properties at room temperature(≥1160 MPa). As the increase of tensile test temperature, the tensile strength of each specimen presented the trend of decreasing, from room temperature to 400℃, the decrease of tensile strength for each sample was not obvious; between 400~600℃, the tensile strength of specimens reduced significantly; At 600℃, the samples could still maintain high strength values(≥780 MPa). The tensile fracture surfaces exhibited the characteristics of quasi-cleavage fracture. In friction and wear experiments, the friction coefficients fluctuated significantly with the change of time, the wear mechanism for the samples were mainly abrasive wear and adhesion wear; with the increase of sintering temperature and reinforcement content, wear resistance of materials first increased and then decreased, the alloy containing 5wt.% WC sintered at 1050℃ had the best wear resistance property.