【作者】 张昕；

【导师】 何长树；

【作者基本信息】 东北大学 ， 材料学， 2009， 硕士

【摘要】 本文利用EBSD、AFM及光学显微镜研究了不同变形量下(2%、5%、10%和30%), Fe-30Mn-4Si-2Al TRIP/TWIP钢(A12钢)和Fe-30Mn-3Si-3Al TWIP钢(A13钢)的组织演变规律和加工硬化机制。在拉伸变形过程中,三种形变产物(平面位错带,ε马氏体和形变孪晶)都沿{111}惯习面产生,并呈现板条状形态。通过测量Al2钢拉伸变形的表面浮凸角发现,在拉伸变形量为10%时,大部分的板条状组织的表面浮凸角度都接近于形变孪晶的理论值。而在基体中新生的板条状组织的表面浮凸角度都接近于ε马氏体的理论值。实验结果表明,随着拉伸变形量的增大,Al2钢的变形机制由应力诱发ε马氏体逐渐转变为应力诱发孪晶。由于Al3钢产生的板条状组织过于“纤细”,大部分的板条状组织无法测量准确的浮凸角度,而少数可以测量的板条状组织的浮凸角度接近于形变孪晶的理论值。利用EBSD研究拉伸变形量为10%及30%的Al2钢发现,当拉伸变形量为10%时,Al2钢中并没有发现形变孪晶,主要的显微组织为应力诱发ε马氏体。当拉伸变形量增大到30%,发现在ε马氏体板条内侧形成了少量形变孪晶。通过EBSD观察发现在拉伸变形量为10%的Al3钢中只形成了少量的形变孪晶。结合Ogawa.Kazuyuki和Sawaguchi. Takahiro的TEM结果证明在小变形量下Al2钢的主要形变组织为ε马氏体,Al3钢的形变组织为形变孪晶及平面位错。尽管拉伸形变的组织不同,但两种钢显示了相似的加工硬化行为。利用EBSD观察了在拉伸变形过后,两不同{111}惯习面的马氏体板条或变形孪晶相交叉的现象。通过晶体学分析,得到以下结论：在Al2钢中两马氏体板条相交叉处形成了二次奥氏体相,这可能是由于不同{111}的两个半孪晶切变相结合的结果。在应力诱发ε马氏体板条内部形成了{1012}hcp孪晶。在Al3钢中两个变形孪晶也同样在交叉处形成了二次奥氏体相,但它的形成机制与马氏体板条相交叉的机制不同,形成机理仍有待进一步研究。更多还原

【Abstract】 The deformation microstructures Fe-30Mn-4Si-2Al TWIP/TRIP steel (A12) and Fe-30Mn-3Si-3Al TWIP steel (A13) with different amount of tensile deformation (2%,5%, 10% and 30%) were investigated by the combined use of optical microscopy (OM), atomic force microscopy(AFM) and electron backscatter diffraction (EBSD) technique. The work hardening mechanism of the A12 and A13 steels were also discussed.Three kinds of deformation structures (the planar dislocation band, the s martensite and the deformation twin) are commonly formed on the{111} habit planes and exhibit plate-like morphology during tensile deformation. The surface tilt angles were determined by AFM for 10% tensile deformed A12 steel. It is found that surface tile angles of most banded structure determined by AFM are closed to the theoretical value of deformation twin. While, the surface tilt angles of the new plates formed in austenite matrix are close to the theoretical value of theεmartensite. Those results indicate, for A12 steel, in the case of small defomation, stress-induced martensite transformation is the dominant deformation mechanism, which alters into deformation twinning as deformation stain increases. Most of banded structures formed in A13 TWIP steel were too thin to precisely determine the surface tile angle by AFM. A few plates with relatively large thicknesses could be selected for the quantitative surface analysis. The values of their surface tilt angles were closed to the theoretical values of deformation twins.Microstructures of tensile deformed A12 steel (with deformation strains of 10% and 30%) were investigated by means of EBSD technique. For 10% tensile deformed A12 steel, fullεmartensite microstructure was observed and no deformation twin was found. As the deformation strain increased to 30%, a small amount of deformation twins were observed between s martensite plates. For 10% tensile deformed A13 steel, it was found that only a small amount of deformation twins was formed during deformation. Based on the TEM analysis taken by Ogawa.Kazuyuki and Sawaguchi.Takahiro, it may conclude that, under small deformation, the microsturcture of A12 steel consists mainly of s martensite, while the microstructure of A13 steel is mainly composed of deformation twin and planar dislocation. Although there is too much deference in microstructures between the two alloys, they exhibit a similar work hardening behavior during tensile deformation.By means of EBSD, the microstructures at intersections between twoεmartensite plates on different{111} habit planes in A12 steel and those between two deformation twin plates in A13 TWIP steel were examined. The following conclusions were made based on crystallographic analysis. It was found that the secondary FCC twin was formed at the intersection between two HCP plates, which could be probably attributed to the combination of two half-twinning shears on different{111} planes.{1012} HCP twinning was also observed inside the stress-induced s martensite plates. The intersecting of two deformation twin plates also brought about the formation of secondary austenite twin, but its formation mechanism may be different from that for the martensite intersecting. The detail is still under analysis.更多还原