The influence of chemical composition of Ni-based alloys on microstructure and mechanical properties of plasma paste borided layers

Plasma paste boriding at temperature of 800 degrees C (1073 K) for 3 h was applied in order to produce hard ceramic phases on the surface of Ni-based alloys with various chromium concentrations. The microstructure of boride layer depended on the chemical composition of substrate material. The increase in chromium concentration was the reason for reducing the average thickness of the boride layers. Hence, the average thicknesses were as follows: 54.24 +/- 3.07 mu m for Nickel 201-alloy, 44.41 +/- 2.24 mu m for Inconel (R) 600-alloy, 41.31 +/- 1.56 mu m for Nimonic (R) 80A-alloy. The chemical and phase composition of the investigated layers strongly influenced their hardness (HVIT), Young's modulus (E-IT) and fracture toughness (K-c). The boride layer, produced on Nickel 201-alloy, was characterized by lowest average hardness of 17.97 +/- 1.59 GPa and Young's modulus of 217.89 +/- 20.72 GPa. The highest values of HVIT and E-IT (22.96 +/- 4.30 GPa and 291.95 +/- 25.64 GPa, respectively) were obtained for boride layer on Nimoni (R) 80A-alloyin which the highest chromium concentration occurred. It was also confirmed that the increase in chromium concentration in substrate material strongly influenced the fracture toughness of the produced layers. The plasma-paste borided layer, in which only nickel borides were identified, was characterized by the highest average fracture toughness (K-c) of 1.477 +/- 0.86 MPa.m(1/2). Whereas, the boride layer on Nimonic (R) 80A-alloy (Cr content of 19.52 wt%) was characterized by about tree time lower fracture toughness (K-c = 0.534 +/- 0.44 MPa.m(1/2)).