Development of a laboratory-based transmission diffraction technique for in situ deformation studies of Mg alloys

A laboratory-based transmission X-ray diffraction technique was developed to measure elastic lattice strains parallel to the loading direction during in situ tensile deformation. High-quality transmission X-ray diffraction data were acquired in a time frame suitable for in situ loading experiments by application of a polycapillary X-ray optic with a conventional laboratory Cu X-ray source. Based on the measurement of two standard reference materials [lanthanum hexaboride (NIST SRM 660b) and silicon (NIST SRM 640c)], precise instrumental alignment and calibration of the transmission diffraction geometry were realized. These results were also confirmed by the equivalent data acquired using the standard Bragg-Brentano measurement geometry. An empirical Caglioti function was employed to describe the instrumental broadening, while an axis of rotation correction was used to measure and correct the specimen displacement from the centre of the goniometer axis. For precise Bragg peak position and hkil intensity information, a line profile fitting methodology was implemented, with Pawley refinement used to measure the sample reference lattice spacings (d o (hkil)). It is shown that the relatively large X-ray probe size available (7 × 714mm) provides a relatively straightforward approach for improving the grain statistics for the study of metal alloys, where grain sizes in excess of 114μm can become problematic for synchrotron-based measurements. This new laboratory-based capability was applied to study the lattice strain evolution during the elastic-plastic transition in extruded and rolled magnesium alloys. A strain resolution of 2 × 10-4 at relatively low 2θ angles (20-65° 2θ) was achieved for the in situ tensile deformation studies. In situ measurement of the elastic lattice strain accommodation with applied stress in the magnesium alloys indicated the activation of dislocation slip and twin deformation mechanisms. Furthermore, measurement of the relative change in the intensity of 0002 and 10 3 was used to quantify {10 2} 011 tensile twin onset and growth with applied load.

In-situ synthesis of titanium carbides in iron alloys using plasma transferred arc welding

The synthesis of Fe-TiC metal matrix composite during metal deposition with laser and arc welding techniques is of technical and economic interest for hard surfacing of engineering components. Recent studies linked the resistance to abrasive wear with the size and morphology of TiC precipitates, which are strongly dependent on the deposition conditions and, more importantly, on the alloy chemistry. In this study, the effect of silicon and manganese on the TiC precipitates was explored and different processing conditions were assessed. The characterisation included optical and scanning electron microscopy, X-ray diffraction and microhardness testing. The results indicate that silicon and manganese can have a significant effect on TiC size and morphology. Therefore, the composition of the matrix alloy offers an effective pathway to modify the microstructure of in-situ precipitated Fe-TiC metal matrix composites. © 2013 Elsevier B.V.