Measurements of residual strains and stresses in laser formed plates of Ti-6Al-4V using synchrotron X-ray diffraction

摘要

The synchrotron X-ray diffraction technique is used to examine the development of residual strains in laser formed plates of the alpha-beta titanium alloy Ti-6Al-4V. The following conditions were studied: (A) one pass of the laser beam; (B) three passes with intervals of 10 s between scans; (C) three passes but with 90 s intervals; (D) five passes with 10 s intervals; and (E) five passes with 90 s intervals. Measurements were made in both the longitudinal and transverse directions using the {101-bar 3} and {112-bar 0} lattice planes. The sample with five passes and 90 s intervals exhibited the largest residual stresses in the longitudinal direction, and the sample with a single pass had the lowest. The width of the zone of tensile strain was largest in the sample with five passes at 10 s intervals; next was the sample with three passes at 10 s intervals. Optical microscopy and microhardness tests demonstrated that the temperature - time history associated with condition D was sufficient to partially anneal the material, and hence low strains were observed. Needle probe distortion measurements showed that condition D resulted in the largest distortion angle (approx 7.0 deg) while the smallest distortion (approx 0.4 deg) was observed after condition A.