The effect of rare earths(La, Ce and Pr) addition on residual stress in iron coatings prepared by brush plating was investigated. The results showed that the addition of rare earth transformed the residual stress in the coating from tensile to compressive. To relieve the residual stress, on the one hand, RE elements segregated at the grain boundaries which restricted the coalescence of the grains and provided more capability of grain deformation. On the other hand, RE elements could purify detrimental element and absorb hydrogen atoms in the coating. Among the three rare earths, elements lanthanum showed the most significant effect on surface morphology and residual stress.
An integrated low temperature nitriding process for TC4(Ti6Al4V) has been developed and the effect on wear resistance has been investigated. Through the process of solid solution strengthening—cold deformation—nitriding at 400 °C, the TC4 alloy is nitrided on surface and dispersion strengthened in bulk at the same time. The white nitriding layer is formed after some time of nitriding. The nitriding speed increases with the deformation degree. The construction was investigated by XRD and the nitride is Ti_3N_(2-X). The wear test was carried out and results exhibit that the nitrided samples have better wear resistance.
