X-RAY STRESS ANALYSIS ON SINGLE CRYSTAL BY USING IMAGING PLATE

利用二维x射线探测器成像板测量了单晶试样或多晶试样中任何单个颗粒的应力。由于没有测量到连续的德拜-施谬（DS）衍射环，而在多晶试样的假想DS圆上只出现了晶粒的一个斑点，因此如何在实验上测量应力是一个问题。因此，校正待测光斑的晶格间距很重要，由于在虚圆上容易得到可测的衍射光斑，所以我们采用了成像板和试样振荡的方法。制备细粒纯铁试样，用劳法测定每个晶粒的取向（hkl） [uvw]后，用Cr-Kalpha x射线测定每个晶粒在塑性变形前后的211次衍射。利用两个步进电机从衍射点转换可测量的电弧，在样品表面的x射线照射点上沿RX-RY方向振荡带有phi和psi旋转附件的样品台。此外，还在同一成像板上衍射了退火铁粉的DS环，以精确测定成像板与试样之间的距离。利用成像板制作衍射图所需的曝光时间小于3分钟，借助图像处理技术精确地确定了晶格间距。塑性变形前后的晶格间距可以确定应力张量，塑性变形后的晶格间距可以确定残余应力张量。由于两个张量之间的差异相对较小，因此我们得出结论，在无应力条件下，无需使用晶格参数即可测量晶粒中的残余应力。

Stresses in a single crystal specimen or any individual grain of polycrystals specimen were measured by the use of imaging plate which is a two-dimensional x-ray detector. A problem is how to measure stresses experimentally because continuous Debye-Scherror (DS) diffraction ring in not measured but only just a spot from a grain is appeared on an imaginary DS circle from polycrystals specimen. Therefore, it is important to correct such spot to be measured lattice spacing and we adopted the imaging plate and a specimen oscillating because it is easy to obtain a measurable diffraction spot on an imaginary circle.Course grained pure iron specimens were prepared and after determination of orientation (hkl) [uvw] on each grain measured by Laue method, 211 diffractions on each grain before and after plastic deformation were measured by Cr-Kalpha x-rays. A sample stage with the phi and psi rotating attachment was oscillated upon the x-ray irradiated point on the specimen surface in RX-RY directions by use of two stepping motors to convert a measurable arc from a diffraction spot. In addition, a DS ring from annealed iron powder was also diffracted on the same imaging plate for precise determination of the distance between imaging plate and specimen.Exposure time required for a diffraction pattern was less than 3 minutes by use of the imaging plate and the lattice spacing was accurately determined by the assistance of the image processing technique. We can determine both the stress tensor from the lattice spacing before and after plastic deformation and residual stress tensor from those after plastic deformation only. Since the difference between both tensors is comparatively small, we concluded that residual stresses in a grain can be measured without the use of lattice parameters on the non-stresses condition.