Limiting energy characteristics during laser pulse treatment of tungsten-cobalt hard alloys

The considered analytical method for determining the optimal mode of hardening pulsed laser treatment (LT) of tungsten-cobalt hard alloys is based on the study of the patterns of temperature field formation during hardening of hard alloys, determination of thermal stresses occurring in the laser exposure zone (LEZ) during laser pulse treatment, and their comparison with the stresses of fracture of the alloy individual structural elements. The optimal modes of hardening LT of the alloys of WC group are considered to be modes that meet two criteria. First, the temperature on the LEZ surface should be in the range of 1290 °C < T < 1400 °C, when the alloy does not contain weakening it phases of the η-Co 3 W 3 C, θ-Co 3 W 2 C, or χ-Co 3 W 9 C 4 types, and increase in grain size of the carbide phase is insignificant. Secondly, cracks of an arbitrary scale are unaccep­table in the LEZ, that is, the thermal stresses resulting from the fracture should not exceed the stresses of fracture of the alloy structural elements. The calculation of thermal stresses occurring in a hard alloy during LT within a single carbide grain was carried out in accordance with the Hooke’s law. Calculations performed for both single and multiple treatments allow us to establish that for all the studied modes, with variations in the laser energy density from 0.9 to 1.8 J/mm 2 and treatment multiplicity from 1 to 10, when the surface temperature is in the range of 1290 – 1400 °C, the thermal stresses in the carbide phase are lower than minimum fracture stresses and do not exceed 80 MPa. The proposed analytical method for determining the limiting energy characteristics makes it possible to establish pulsed LT modes that provide dispersion hardening of hard alloys of the WC group in the absence of destructive changes in the material. The data obtained on defect-free LT modes are in good agreement with the earlier results of measurements of acoustic emission signals during treatment of hard alloys (VK8 alloy).