Stresses in laser alloyed surfaces of high-melting metals

Ryszard Pawlak; Maria Walczak

doi:10.1117/12.287821

3 October 1997 Stresses in laser alloyed surfaces of high-melting metals

Ryszard Pawlak, Maria Walczak

Proceedings Volume 3187, Laser Technology V: Applications in Materials Sciences and Engineering; (1997) https://doi.org/10.1117/12.287821
Event: Laser Technology V, 1996, Szczecin, Poland

Abstract

The paper deals with stresses induced in the alloyed layers of high-melting metals in the laser treatment process with a continuous beam and a pulse of a duration (tau) equals 4 ms. It has been found that the threshold power densities of laser radiation resulting in the permanent plastic strain of the metal under treatment are greater than the ones used during treatment. Making use of an analysis of the temperature field, the cooling rates of the treated zone have been determined by the finite difference method and an analytical method. The spatial non-uniformity of the heating and cooling rate of tungsten and molybdenum can be the cause of plastic strain and fractures on the metal surface. Experimental investigations were carried out for the optimal parameters of a laser radiation beam (the maximum depth of the alloyed layer, possibly with the smallest number of fractures). A privileged direction of fractures at an angle of 45 degrees in relation to the direction of scanning was observed (basing on the microscopic observations of 2 mm by 2 mm layers made on the surface of 10 specimens). Experiments showed a considerable effect of the type of the metals treated on the likelihood of occurrence of fractures; these are distinct and numerous in the case of molybdenum alloyed with nickel, whereas they cannot be observed in tungsten alloyed with nickel at a magnification of X 20,000. The smaller concentration of stresses in tungsten is also confirmed by the results of microhardness measurements (Table 2). The different behavior of the metals under treatment may be caused by volumetric changes brought about by metallurgical phase transitions.

Citation Download Citation

Ryszard Pawlak and Maria Walczak "Stresses in laser alloyed surfaces of high-melting metals", Proc. SPIE 3187, Laser Technology V: Applications in Materials Sciences and Engineering, (3 October 1997); https://doi.org/10.1117/12.287821

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