The effect of microstructures on the fatigue crack growth in Ti-6Al-4V laser welds

Abstract

The effect of microstructures on fatigue crack growth rates (FCGRs) in Ti-6Al-4V plates and laser welds was investigated. Experimental results revealed that the location of tensile fracture of laser-welded specimens was always in the base metal, owing to the presence of martensite in the narrow fusion zone (FZ). For welds aged at various temperatures, only minor differences in tensile properties were observed. The various heat treatments of such plate did not affect FCGRs significantly. The fracture surface was characterized by fatigue striation at high Delta K values. When the R ratio was increased from 0.1 to 0.4, higher FCGRs would be resulted. The decomposition of martensite in the aged FZ causes retardation of FCGRs in a weld, which is characterized by a mixed mode fracture. The more tortuous crack path within the FZ and HAZ was also indicative of high crack growth resistance. Roughness-induced crack closure caused by crystallographic fracture was responsible for decreased FCGRs. (C) 1998 Elsevier Science Ltd. All rights reserved.