Application of spark plasma sintering (SPS) for the fabrication of in situ Ni–TiC nanocomposite clad layer

Highlights: • Direct and indirect mechanical alloying was applied to fabricate a Ni–Ti–C metastable powder. • The metastable mechanically alloyed powder could undergo a reaction to synthesize TiC at high temperatures. • Spark plasma sintering was proposed as a cladding method to fabricate in situ Ni–TiC composite layer on steel. - Abstract: Spark plasma sintering (SPS) was utilized to create in situ Ni–TiC nanocomposite layers on steel substrates using reactive powders. Reactive Ni–Ti–C powders with a nominal composition of Ni–40 wt.%TiC were prepared by mechanical alloying (MA) in a high energy planetary ball mill. Two approaches were applied to prepare reactive powders. In the first approach a single-step method was conducted by milling Ni, Ti and C simultaneously. The second approach involved double step MA in which Ni–Ti and Ni–C powder mixtures were milled separately in the first step and the resultant powders were mixed and re-milled in the second step. Reactive powders were sintered successfully on St37 steel substrates by spark plasma sintering technique. X-ray diffractometery (XRD) was used to study the structural evolution during milling and after sintering. Powder particles and clad layers were examined by scanning electron microscopy (SEM) for microstructural investigations. Hardness measurements were conducted on the cross section of powder particles and clad layers. Sintering of reactive powders led to the in situ formation of TiC nano particles within the Ni matrix. Also the hardness of SPSed clad layers obtained from single step and double step MAed powders increased to 1250 and 780 HV, respectively. Clad layers showed a defect free interface with the steel substrate