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

A one-dimensional, transient, inverse heat conduction problem is implemente d to investigate the influence of temperature and surface conditions on sur face absorptivity in the laser surface heating process. Analysis includes t he utilization of the conjugate gradient method (CGM), with temperatures me asured near the heated surface. To increase efficiency and accuracy of the calculation, the result retrieved from the least-square method is used as a n initial guess for the CGM. Results show that absorptivity decreases when the temperature exceeds a certain value. This decrease is related to struct ural transformation during the temperature rise. As the surface temperature nears the melting point, the decreasing trend inverts and absorptivity inc reases. This final abrupt rise is caused by the phase transformation from o rder to disorder. Additionally, absorptivity is related to surface conditio ns such as absorption-enhancing coatings and surface roughness. (C) 2000 Am erican Institute of Physics. [S0021-8979(00)02307-0].