Luo Xinmin

Stacking fault energy of cryogenic austenitic steels

Stacking fault energy and stacking fault nucleation energy are defined in terms of the physical nature of stacking faults and stacking fault energy and the measuring basis for stacking fault energy. Large quantities of experimental results are processed with the aid of a computer and an expression for calculating stacking fault energy has been obtained as γ300SF (mJ m-2) = γ0SF + 1.59Ni - 1.34Mn + 0.06Mn2 - 1.75Cr + 0.01Cr2 + 15.21Mo - 5.59Si -60.69(C + 1.2N)1/2 + 26.27(C + 1.2N)(Cr + Mn + Mo)1/2 + 0.61[Ni(Cr + Mn)]1/2.

DISLOCATION MECHANISM OF SURFACE MODIFICATION FOR COMMERCIAL PURITY ALUMINUM AND ALUMINUM ALLOY BY LASER SHOCK PROCESSING

Surface modification experiment of the commercial purity aluminum(α-Al) and AlCu -Mg alloyed aviation aluminum alloy 2A02 by laser shock processing(LSP) was implemented.The surface strengthening effect of both the target materials was investigated from dislocation mechanisms of microstructural response by means of TEM method.The results show that the strengthening effect of the two kinds of materials by laser shock processed is significantly different.The strengthening mechanism of a-Al by laser shock can be attributed to the multiplication of a large number of dislocations. With the increase of the impact number of laser shock and the degree of deformation,the new-generated dislocations will pile up and interact with the forest dislocations,and the dislocation lines will gradually evolve into waved-like,or wind into dislocation tangles and dislocation networks. But the hardness curve of the laser shocked(α-Al) will fast and linearly decline due to Bauschinger effect(BE) and stress wave damping.The laser shock strengthening mechanisms of the aging-hardened aluminum alloy 2A02 can be summarized to the enhancement of the matching between the elastic energy of dislocations with the ultra-high energy of laser shock processing due to the higher matrix strength and the dislocation-pinning effect of large number of dispersed precipitates,as well as the complex dislocation networks in between the precipitates constructed by the dislocations induced by laser shock. The matrix strengthened by laser shock processing and the precipitates keep the extra-semi-coherent relationship to coordinate the total deformation,with the number of laser shock increase,dislocation multiplication and the vacancy motion constitutes geometrically necessary boundaries(GNBs),which consists of the sub-grain boundaries to refine the matrix into the nanometer-grains.The strengthening mechanism of surface modification of aluminum alloy by laser shock processing is formed of the internal stress state caused by the combination of the complex dislocation configurations and the Hall-Petch effect of the nanocrystalline grains.

Microstructure Characterization of Titanium Alloy Sheet by Laser Shocking

The TA2 (ASTM F67 Grade 2)Titanium alloy sheet was laser shock deformed by the Nd: YAG laser with the 1054nm output wave length and the 20ns short pulse, with 7 mm laser facular in diameter and tap water as the confinement regime. The experimental results indicated that under the available constraint condition, the obverse and the deformation was sensitive to the strain types. Strain-induced marten site in the compressive-stressed region, and the strain-induced twins in the tensile-stressed region were observed respectively. The super-high energy and super high strain ratio upon laser shock deforming can make the c.p.h. titanium alloy induce a great deal of twin bands, which coordinate the orientations in grains, thus induce auxiliary slip systems operate and make the plastic deformation proceed.