Time- and temperature-resolved synchrotron X-ray diffraction: observation of phase transformation and strain evolution in novel low temperature transformation weld filler materials
Time- and temperature-resolved synchrotron X-ray diffraction: observation of phase transformation and strain evolution in novel low temperature transformation weld filler materials
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时间和温度分辨同步加速器 X 射线衍射：观察新型低温转变焊接填充材料的相变和应变演化
DOI：
10.1177/0309324711413190
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
A. Wanner
中科院分区：
文献类型：
--
作者：
J. Altenkirch;J. Gibmeier;V. Kostov;A. Kromm;T. Kannengiesser;S. Doyle;A. Wanner
利用卡尔斯鲁厄理工学院(Karlsruhe Institute For Technology)同步辐射光源ANKA(Angströmquelle Karlsruhe)的PDIFF(粉末衍射)光束线上的创新实验装置，实时监测了新型低温转变(LTT)焊接填充材料近表面区域的固态相变以及热应变和弹性应变的演变。衍射仪的关键部件是两个快速的微带线探测器，它可以跟踪应变随时间和温度的变化，S计数时间为0.5 。在受控加热和冷却循环以及临近焊接循环期间，分析了马氏体-奥氏体-马氏体相变。利用专门设计的用于现场衍射仪研究的焊接试验台，监测了纯LTT合金小切屑的电阻加热过程和简化LTT焊缝的钨极气体保护焊过程中的相变动力学。在允许自由热膨胀和自由收缩的机械约束条件下，随着Ni含量的增加，LTT合金的相变温度Ac和Ms降低，残余奥氏体相含量增加。焊接过程中的应变演化表明，焊接时的压应力增加，这归因于冷却时形成的马氏体，抵消了热收缩应变。相变温度的比较表明，LTT合金的相变温度高于纯LTT合金，但不同合金之间没有变化。一方面，这是由于择优取向影响了衍射测量和相变温度的确定。另一方面，随着LTT合金化学成分的不同以及焊接过程中的机械约束，残余应变和应力的演变可能会有所不同，从而导致马氏体起始温度降低的相反影响。
Solid-state phase transformations and the evolution of thermal and elastic strains in novel low temperature transformation (LTT) weld filler materials in the near surface region are monitored in real time by means of an innovative experimental set-up at the PDIFF (powder diffraction) beamline at the synchrotron light source ANKA (Angströmquelle Karlsruhe) at the KIT (Karlsruhe Institute for Technology). The key components of the diffraction set-up are two fast microstrip line detectors, which enables the strain evolution to be followed as a function of time and temperature for a 0.5 s counting time. During controlled heating and cooling cycles, as well as during near welding cycles, the martensite–austenite–martensite phase transitions are analysed. The transformation kinetics are monitored during resistance heating of small chips of the pure LTT alloys and during gas tungsten arc welding of simplified LTT welds using a specially designed welding rig for in-situ studies on the diffraction instruments. Under the mechanically unconstrained condition allowing free thermal expansion and shrinkage, the LTT alloys are found to exhibit decreasing transformation temperatures Ac and MS and increasing phase fraction of retained austenite for increasing Ni content. The strain evolution during welding reveals increased compressive stresses upon welding, which is attributed to the martensite formation upon cooling, which counteracts the thermal contraction strains. Comparison of the transformation temperatures reveals higher values than in the pure LTT alloys, but no variation between the different alloys. On the one hand, this is attributed to preferred grain orientation affecting the diffraction measurements and the determination of the transformation temperatures. On the other hand, it is possible that with the different chemical compositions of the LTT alloys and the mechanical constraints during welding, the evolution of the residual strain and stress may vary and result in counteracting affects with respect to lowered martensite start temperatures.