| Fe-Al alloy has excellent high temperature oxidation resistance, wear resistance and corrosionresistance. However, due to the drawbacks of poor tenacity and being difficult to manufacture andprocess, its application and development have been restricted severely. Previous studies have shownthat Cr can improve the plasticity of the Fe-Al alloy effectively. In the mean time, it can furtherimprove the comprehensive properties of the Fe-Al alloy. Using surface alloying technology toprepare Fe-Al-Cr alloyed layer onto the surface of the ordinary tenacious substrate can not only exertthe excellent properties of the Fe-Al alloy but also avoid the problem of being difficult to process ofthe whole material.In this paper, double glow plasma surface metallurgical technology was exploited to prepare theFe-Al-Cr alloyed layer onto the surface of the Q235carbon steel. The optimal process parameterswere explored as follows: source electrode voltage:850～950V; substrate electrode voltage:450～550V; testing temperature:800°C; operating time:3.5h; operating atmospheric pressure:35Pa; andinter-electrode distance:15mm. Then, SEM, EDS, XRD, scratch test, microhardness test,nanoindentation test, isothermal oxidation test, frictional wear, and electrochemical corrosion test etcwere carried out to further investigate and analyze the microstructure, composition distribution,organization structure, mechanical properties, high temperature oxidation resistance, wear resistanceand corrosion resistance of the alloyed layer prepared under optimal conditions. It was found that thebinding between the alloyed layer and the substrate was fine, which was metallurgical binding. Thethickness of the as-prepared alloyed layer under these conditions was25~30μm. The alloyed layerwas uniform and impact without any defects of porosities and cracks. The elements in the alloyedlayer exhibited gradient distribution from the exterior surface to the inner layer. Specifically, Feexperienced a upward trend, while Cr displayed a opposite trend. However, the tendency of Alshowed a increase before a decrease. The main phases of the alloyed layer were Fe2AlCr, Fe3Al, FeAl,Fe(Cr) sosoloid, Cr23C6and α-Fe(Al). The surface microhardness of the alloyed layer was460.3HV0.1,which was2.5times higher than that of the substrate. The elasticity modulus of the alloyed layer was284.2GPa and the plastic deformation work was5.68×10-8J, implying that it had the capacity to resistplastic deformation and its tenacity increased. The high temperature oxidation tests demonstrated thatthe high temperature oxidation resistance of the Fe-Al-Cr alloyed layer at the temperatures of500,600, and700°C increased dramatically as compared to the substrate. The oxidation film of the Fe-Al-Cr alloyed layer had a self-healing ability. According to the frictional wear tests, under differentloading and temperatures, the frictional coefficient, wear rate, wear volume and specific wear rate ofthe Fe-Al-Cr alloyed layer were all lower than those of the substrate. Under conditions of themaximum loading (530g) and the highest temperature (400°C), the frictional coefficients of theFe-Al-Cr alloyed layer were0.2758×10-3mm3N-1m-1and0.1656×10-3mm3N-1m-1, which were1/3and1/5as large as those of the substrate, respectively. These indicated that this alloyed layer couldenhance the wear resistance of the substrate drastically. The electrochemical tests showed that the selfcorrosion potential (Ecorr), the self corrosion current (icorr), and the polarization resistance (Rp) of theFe-Al-Cr alloyed layer in a solution with3.5%NaCl were-0.348V,1.245×10-3A/cm2and248.9Ω/cm2,repectively. These data were better than those of the substrate and the304steel. While, in the solutionwith0.5mol/L H2SO4, under the condtions of a maintaining passivity potential and current density as-0.201V and3.120×10-3A/cm2, a passivation film formed on the surface of the Fe-Al-Cr alloyed layerthat could impede the erosion effect of the corrosive medium, which effectively protected thesubstrate from being eroded. |
PDF Full Text Request