Correlation of real-time thermal history with tribological properties of laser coated NiCrBSi with Ag and WS2 addition

Abstract

The laser coating of NiCrBSi in pure form as well as with the addition of lubricious Ag or WS 2 has been developed on Ti6Al4V substrate. With the help of an IR pyrometer , real-time thermal history was monitored and correlated with the tribological properties of the coating. A matrix predominantly comprised of NiTi and NiTi 2 and reinforced with hard phases like CrB, TiC, TiB 2 , Cr 3 C 2 was formed for all the types of coatings. From the XRD and EDS analysis, it was observed that for the coating containing Ag, Ag was found to be present in elemental form, but in the case of coating containing WS 2 , WS 2 got dissociated during laser processing and formed TiS 2 , an anti-friction phase. Effects of heat input on the tribological behavior of both types of coatings (in-situ generated lubricating phase TiS 2 and ex-situ developed lubricating phase Ag) were analyzed with the help of real-time thermal history. For Ag-type coating, maximum hardness, minimum COF and, minimum wear rate were obtained as 968 HV, 0.25, and 2.21E-5 mm 3 /N-m respectively for lower power and higher velocity process parameters. For WS 2 coating, maximum hardness, minimum COF and, minimum wear rate were obtained as 1303 HV, 0.26, and 1.5E-4 mm 3 /N-m respectively for lower laser power and higher scan speed. Comparing both the coating, it can be stated that, low heat input led to a high cooling rate, low molten pool life, and a low peak temperature of the molten pool, which increased the lubricious phase in the coating thereby reducing the friction coefficient. The present study can be useful to develop the process maps for desired lubrication property of the coating by using real-time monitoring of the thermal histories during the laser coating process . • Correlation of real-time thermal history with performance of the laser coatings • Laser coating of NiCrBSi with addition of Ag and WS 2 as solid lubricant • Shorter molten pool life time and low peak temperature reduced friction. • Process map based on the correlation of online monitoring and tribological property • Minimum COF and wear rate of the coating was 0.25 and 2.21E-5 mm 3 /N-m respectively.