Microstructure And Properties Of(WC+η)Reinforc-Ed Iron Matrix Composites Prepared By In Situ Plasma Ra-Diation

Tungsten carbide reinforced iron matrix composites with high hardness,high modulus and excellent wear resistance are widely used in metallurgy,mining and other important fields of national economy.However,due to the mismatch of physical parameters such as hardness,thermal expansion coefficient and modulus between tungsten carbide and iron matrix,the stress concentration at the interface between tungsten carbide and iron matrix is easy to crack and lead to material failure during the process of deformation caused by external force.In this paper,η phase is introduced,(WC+η)reinforced phase is designed,and(WC+η)reinforced iron matrix composites are prepared by hot pressing sintering method and plasma radiation technology.SEM,XRD,EDS and other detection technologies are used to study the effects of different process sequences,different C/W ratios and heat treatment processes on the microstructure and phase composition of the composites.The formation mechanism of reinforcing phase was analyzed.The hardness and bending properties of the composites were tested by Rockwell hardness tester,microhardness tester and universal testing machine,and the bending fracture morphology was characterized to analyze the strengthening mechanism of the composites.The main results of this paper are as follows:(1)(WC+η)reinforced iron matrix composites are composed of η phases,WC and α-Fe,and the interface between the reinforced phase and matrix is well bonded.The preparation process sequence has great influence on the microstructure and density of the composites.Compared with the process of"plasma radiation+hot pressing sintering".the proportion of reinforcing phases WC and η in the composites prepared by "hot pressing sintering+plasma radiation" is more reasonable;The grain sizes of the reinforcing phases WC and η are smaller(<5 μm);The density of the composite material is increased to 91%-92%.(2)With the increase of C/W ratio(0.8～1.2),the carbon content in the system increases,and theη phase changes to WC,the volume proportion of WC increases from 1.46%～2.34%to 34.66%～35.15,and the volume proportion of η decreases from 35.73%～36.61%to 5.41%～6.75%.The formation mechanism of the reinforced phase of composites is mainly the in-situ reaction controlled by C atom diffusion,namely C+W→WC,2W+C→W2C,6Fe+3W2C→2Fe3W3C,Fe3W3C+2C→3Fe+3WC.(3)With the increase of C/W ratio and the increase of carbon content in the system the volume proportion of η of the reinforced phase of the composite decreases,and the bending strength and Rockwell hardness of the composite materials increase first and then decrease.η/(η+WC)=72.10%～76.32%in C/W=1.l composites,and the best bending strength and Rockwell hardness are 1883 MPa and 41 HRC,respectively.(4)After quenching at 950 ℃,the matrix structure of the C/W=1.1 composite material changes from pearlite and ferrite to quenched martensite and residual austenite.The average hardness of the matrix increases from 287 HV0.1 to 574 HV0.1,which is twice as high as that before quenching,and the Rockwell hardness increases to 44 HRC.At the same time,the bending strength of the composites increased from 1883 MPa before quenching to 2187 MPa.(5)The analysis of bending fracture morphology of the composites shows that the reinforcing phase(WC+η)belongs to brittle fracture,the matrix belongs to quasi-cleavage fracture,and the composites fracture is a mixed fracture with the coexistence of two fracture modes.The main strengthening mechanisms of the composites are load transfer strengthening and phase transformation strengthening.