Influence of thermal effects on the micromechanical properties of the nickel-chromium coating obtained by gas powder laser cladding
Introduction. Nickel-chromium coatings can be used in parts that are operated at high temperatures (hot deformation dies, rolls of rolling mills, live rolls, parts of turbines, heat exchangers, etc.). A promising method of coating deposition is gas powder laser cladding, which forms coatings with increased hardness and uniformity. A modern method for evaluating the mechanical properties of nickel-chromium coatings is instrumental microindentation, which records diagrams during loading and unloading of the indenter. The aim of the work is to study the effect of thermal action in the temperature range of 800…1050 °C on the micromechanical properties of the NiCrBSi coating PG-10N-01 obtained by gas powder laser cladding. Methods of research are instrumental microindentation and scanning electron microscopy using energy-dispersive microanalysis. Results and discussion. Thermal action at a temperature of 800 °C only slightly reduces the strength characteristics of the coating, while the dissolution of the strengthening phases in the structure of the coating when heated to 900 °C leads to a significant decrease in the hardness characteristics and parameters that characterize the resistance to elastic-plastic deformation. The formation of a “frame-like” structure with a base of large carboborides Cr2(B,C) and borides Cr2B with increased elastic moduli upon heating to 1050 °C (holding for 1 h, cooling in air) leads to a strong increase in the average contact elastic modulus to ~ 280 GPa (with an average level of elastic modulus of ~ 200 GPa in the coating after cladding and after additional heating to 800 and 900 °C). Also, the strength characteristics of microindentation (Martens hardness and indentation hardness at maximum load) and calculated parameters that indicate the improved ability of the coating with a “frame-like” structure to deform in a “favorable” elastic region, as well as to resist mechanical contact loads even after the beginning of the plastic flow, grow to maximum values.