TA15钛合金中纳米压痕附近残余应力应变场及几何必须位错密度的分布(英文)

ELSEVIER PressAvailable on line at www.sciencedired.comScienceDirectTransactions of Nonferrous Metals Society of ChinaTrans. Nonferrous Met. Soc. China 23(2013) 7-13www.inmsc.cnResidual elastic stress-strain field and geometrically necessary dislocationdensity distribution around nano-indentation in TA15 titanium alloyDong HE, Jing-chuan ZHU, Zhong-hong LAI, Yong LIU, Xia-wci YANG, Zhi-sheng NONGSchool of Materials Science and Engineering, Harbin Institute ofTechnology, Harbin 150001, ChinaReceived 5 December 2011; accepted 16 February 2012Abstract: Nanoindentation and high resolution electron backscatter diffraction (EBSD) were combined to examine the elastic modulus and hardness of a and 0 phases, anisotropy in residual clastic stress-strain fields and distributions of geometrically necessary dislocation (GND) density around the indentations within TAI5 titanium allcy. The nano-indention tests were conducted on a and 0 phases, respectively. The residual stress-strain fields surrounding the indentation were calculated through crosscorrelation method from recorded patterns The GND density distribution around the indentation was calculated based on the strain gradient theories to reveal the micro-mechanism of plastic deformation The results indicate that the elastic modulus and hardness for a phase are 129.05 GPas and 6.44 GPa, while for 0 phase, their values are 109.80 GPa and 4.29 GPa. respectively. The residual Mises stress distribution around the indentation is relatively heterogeneous and significantly influenced by neighboring soft 卩 phase. The region with low residual stress around the indentation is accompanied with markedly high (a) type and prismatic-GND density Key words: nano-hardness; stress-strain fields; geometrically necessary dislocation; nanoindentation; electron backscaner diffraction; TA 15 titanium alloyand plastic role in the alloy parts, and near a1 IntroductionTA15, whose nominal chemical component is Ti-6A1 -2ZrTMoTV, was developed as BT20 alloy by Russia in 1964 I. As a typical near a titanium, it is a classic high-temperature alloy since it combines the excellent creep behavior of a titanium alloys with the high strength of a协 titanium alloys 2. Therefore, TA15 is preferentially used in aerospace, such as the compressor blades, compressor disks of gas turbine engine and large front fan of modem jet engines 3-5Generally, the microstructure of TA15 titanium consists of dominant coarse a phase (hexagonal close- packed, HCP) lamellae and a few retained 0 phase (body-centered cubic, BCC) layers (less than 10% in volume fraction) 1,5. Because a is the dominant component of phase, its mechanical deformation proprieties play a decisive in-service properties of TAI5 titanium However, the plastic deformation of a titanium alloys is usually poor because of relative high critical resolved stress (CRSS), low numbers of slip systems and poor symmetry for hep lattice structure 6.On the other hand, because of the poor symmetry of the HCP crystal structure, the crystal orientation also has a significant influence on the elastic-plastic deformation response of a phase 7. Furthermore, although the content of p phase is relatively low, it has a significant influence on the dislocation transmission and strainstress compatibility during the plastic deformation or forming process 8. Therefore, it is very important to conduct deep and full mechanical response study on the a and 0 phases in titanium alloysNanoindentation is an instrumented hardness testing technique, with precise indent location, high resolution load control and displacement measurement 9 It is widely used to evaluate the elastic modulus, hardness, local mechanical properties, elastic-plastic responses and micro-heterogeneity properties in materials science 10,11. Over the last two decades, electron backscattered diffraction (EBSD) has been developed to be a worldwide available and relatively easy-to-use technique to characterize the microstructure property Actually, EBSD method not only offers the microstructure and crystal orientation information, but also can be used to study the plastic equivalent strain, Mises stress distribution at grain scale 12 and even theCorresponding author: Jing-chuan ZHU; Tel: +8645186413792; Fax: +86451 86413922. E-mail: fgmshit.cdu.cn DOI: 10.1016/S1003326( 13)62422-X