The influence of temperature and surface conditions on surface absorptivity in laser surface treatment

A one-dimensional, transient, inverse heat conduction problem is implemented to investigate the influence of temperature and surface conditions on surface absorptivity in the laser surface heating process. Analysis includes the utilization of the conjugate gradient method (CGM), with temperatures measured near the heated surface. To increase efficiency and accuracy of the calculation, the result retrieved from the least-square method is used as an initial guess for the CGM. Results show that absorptivity decreases when the temperature exceeds a certain value. This decrease is related to structural transformation during the temperature rise. As the surface temperature nears the melting point, the decreasing trend inverts and absorptivity increases. This final abrupt rise is caused by the phase transformation from order to disorder. Additionally, absorptivity is related to surface conditions such as absorption-enhancing coatings and surface roughness. (C) 2000 American Institute of Physics. [S0021-8979(00)02307-0].