摘要
The creep deformation of two near γ titanium aluminide alloys with equiaxed and lamellar structures have been studied to understand their behaviour as a function of microstructural evolution during the early stages of creep. The lamellar alloys exhibit more pronounced hardening during the primary stage of creep leading to a much better creep resistance and a minimum creep rate two orders of magnitude lower than that of the equiaxed alloys. TEM observations have confirmed that the active deformation mechanisms are the same for both alloys and microstructural states, namely extensive slip of single 1/2〈110〉 dislocations and mechanical twinning. The latter has been comfirmed to occur in a fraction of the grains that never exceeds 50% while 1/2〈110〉 dislocations are active within all the γ grains. The twins are only responsible for a small amount of strain but they lead to a subdivision of the microstructure and determine (directly or indirectly) the hardening process observed during the primary stage of creep. During the secondary stage the creep rate is determined by the unblocking of pinned dislocations by processes such as a pipe diffusion or cross slip that allow thermally activated glide of 1/2〈110〉 dislocations within the γ matrix.
The creep deformation of two near γ titanium aluminide alloys with equiaxed and lamellar structures have been studied to understand their behaviour as a function of microstructural evolution during the early stages of creep. The lamellar alloys exhibit more pronounced hardening during the primary stage of creep leading to a much better creep resistance and a minimum creep rate two orders of magnitude lower than that of the equiaxed alloys. TEM observations have confirmed that the active deformation mechanisms are the same for both alloys and microstructural states, namely extensive slip of single 1/2〈110〉 dislocations and mechanical twinning. The latter has been comfirmed to occur in a fraction of the grains that never exceeds 50% while 1/2〈110〉 dislocations are active within all the γ grains. The twins are only responsible for a small amount of strain but they lead to a subdivision of the microstructure and determine (directly or indirectly) the hardening process observed during the primary stage of creep. During the secondary stage the creep rate is determined by the unblocking of pinned dislocations by processes such as a pipe diffusion or cross slip that allow thermally activated glide of 1/2〈110〉 dislocations within the γ matrix.
出处
《中国有色金属学会会刊：英文版》
CSCD
1999年第S1期244-253,共10页
Transactions of Nonferrous Metals Society of China
