Examination of thermal properties by scanning thermal microscopy in ultrafine-grained pure titanium surface layer produced by surface mechanical attrition treatment

Ultrafine-grained pure titanium surface layer produced by surface mechanical attrition treatment (SMAT) was systematically studied by scanning thermal microscopy (SThM) that allows thermal conductivity to be mapped down to the submicrometer scale. It is found that the microstructures obtained by SMAT show different thermal conductivities that strongly depend on the grain size: the thermal conductivity of the nanostructured surface layer decreases substantially if compared with that of the coarse-grained matrix of the sample. A theoretical approach, based on this investigation, was used to calculate the heat flows from the probe tip to the sample and then estimate the thermal conductivities at different scanning locations. Experimental results and theoretical calculation demonstrate that the SThM analyses can be used as a powerful tool for the thermal property and microstructure analysis of ultrafine-grained microstructures.