The microhardness distribution of the diode laser epitaxially deposited IN718 alloy coating was investigated. The Laves concentration in different regions of the coating was measured by binarization processing. The strengthening phase of the coating was characterized by transmission electron microscopy （TEM）. The results showed that the microhardness increased along the depth of the coating. Part of Laves dissolved into austenitic matrix during the successive laser deposition, A little amount of strengthening phase was precipitated in the bottom region of the coating. It was attributed to the heat effect from the thermal cycle of successive deposition on the microstructure in the bottom region of the epitaxially deposited coating.
The fabrication of high volume fraction （HVF） M7C3 （M=Cr, Fe） reinforced Fe-based composite coating on ASTM A36 steel plate using plasma transferred arc （PTA） welding was studied. The results showed that the volume fraction of carbide M7C3 was more than sixty percent, and the relative wear resistance of the coating tested on a block-on-ring dry sliding tester at constant load （100 N） and variable loads （from 100 to 300 N） respectively was about 9 and 14 times higher than that of non-reinforced a-Fe coating. In addition, under constant load condition the friction coefficients （FCs） of two coatings increased first and then decreased with increasing sliding distance. However, under variable loads condition the FCs of non-reinforced a-Fe based coating increased gradually, while that of HVF MTC3 reinforced coating decreased as the load exceeded 220 N. The worn surface of non-reinforced a-Fe based coating was easily deformed and grooved, while that of the HVF M7C3 reinforced coating was difficult to be deformed and grooved.
