In-process monitoring of distortion and temperature in multi-layer laser cladding of Stellite 6 and Inconel 718 alloys

In laser cladding, the development of rapid heating and cooling cycles generates high residual stresses and thermal gradients that lead to induce unwanted distortion in the parts. The paper deals with online monitoring of temperatures and the associated distortions in multi-layer laser cladding using pyrometers and laser displacement sensors. The alloys deposited in the present work are Stellite 6 and Inconel 718, having similar thermo-mechanical properties. The results show that variation in thermal gradients due to rapid heating and cooling allows the material to expand and contract, generating substantial distortions. In the current investigations, Stellite 6 deposits generated 28%, 21%, 15% higher deflection at 12 mm/s, 16 mm/s, 20 mm/s scan speeds respectively; and 23%, 20%, 17% at 2400 W, 2900 W, 3400 W laser power compared to Inconel 718. Irrespective of the coating material, the second layer cladding induced 10% to 30% lower distortion than the first layer because of the reduction in temperature gradient. However, Inconel 718 clads measured 10% to 15% less melt pool temperatures than Stellite 6. The study reveals that different cladding materials deposited under similar process conditions have greater impact on distortion and temperature. At last, the investigations provide an optimum set of parameters to produce homogeneous cladding with moderate deflection and temperature for both the alloys.