Fracture toughness and yield strength of boron-doped, high (Ti+Mn)Ll(2) titanium trialuminides

Three batches of L1(2)-base titanium trialuminide alloys. one with low Ti c ontent. 9 Mn 25 Ti, and the other two with high Ti content: 14 Mn-29 Ti and 18 Mn-32 Ti (at.%), referred to as 9 Mn, 14 Mn and 18 Mn. respectively. so me doped with 0.004 to 0.66 at.% boron, were induction melted under high pu rity argon, homogenized and subsequently HIP-ed at 1250C/2 h/180 MPa. Both Vickers microhardness and compressive 0.2% offset yield strength ar room te mperature increase primarily with increasing Ti concentration in the L1(2) matrix and secondarily with boron doping, attaining 550 MPa. The yield stre ngth increment by boron doping for high Ti 14 Mn 15 much higher (similar to 1.74 MPa/0.01 at.% B) than that for low Ti 9 Mn (similar to0.1 MPa/0.01 at. % B). At room temperature, a combination of high Ti concentration and boron doping increases chevron-notched beam (CNB) fracture toughness to similar to8 MPa m(1 2)(a 100% increase with respect to low Ti 9 Mn alloy) but fract ure mode remains transgranular cleavage regardless of the composition, At 8 00-1000 degreesC the toughness increase of high Ti 14 Mn is mainly determin ed by a high Ti concentration. For boron-free and borun-doped high Ti 14 Mn the transgranular cleavage/intergranular transition temperature approaches similar to 600 degreesC and at 1000 degreesC the fraction of intergranular failure mode is suppressed to barely similar to 45% (C) 2001 Elsevier Scie nce Ltd. All rights reserved.