Laser compression of monocrystalline tantalum

Abstract

[111] was subjected to laser driven compression at laser energies of 350 to 685 J, generating shock amplitudes varying from 15 to 100 GPa. The laser beam, with a beam spot diameter of ~1 mm, created a crater of significant depth (~ 80 to ~ 200 μm). Twins were observed just below the crater surface (~ 42 μm) by back-scattered SEM. Transmission electron microscopy (TEM) revealed profuse mechanical twinning within a distance from the energy deposition surface of ~ 1.5 mm at 684 J compression power, corresponding to an approximate pressure of 35 GPa. The decay of the pulse through the specimens was accompanied by an attendant decrease in the density of shock-generated dislocations. Microhardness measurements were conducted on the recovered samples. The experimentally measured dislocation densities and threshold stress for twinning are compared with predictions using analyses based on the constitutive response and the similarities and differences are discussed in terms of the mechanisms of defect generation.

Growth and collapse of nanovoids in tantalum monocrystals

“…18. The predicted transition strain rates in compression (1 Â 10 7 s À1 ) is in qualitative agreement with experimental values [69], although the predicted transition strain rate in tension (4 Â 10 2 s À1 ) is much lower than the simulation result (10 8 -10 9 s À1 ). Considering the many simplifications in the current analysis, the results are in qualitative agreement with the analysis above.…”

“…Although the MD simulations did not produce twinning under compression of the voids, it can occur experimentally if sufficiently high shear stresses are reached, as demonstrated by shock compression experiments on Ta crystals in gas guns [65,73] and lasers [69] in which stresses as high as 100 GPa can be reached.…”

“…The value of C 4 was changed from its original value of 0.000327 K À1 to 0.00024 K À1 to fit the results of Rittel et al [68] at both low and high strain rates (solid circles and dash line in Fig. 18), and details are given in a separate paper discussing experimental results [69]. Sherwood et al [70] observed slip and twinning in both tension and compression of [1 0 0] monocrystals, therefore their experimental results are used in this analysis.…”

The defect evolution in shock loaded tantalum single crystals

“…The threshold pressure of tantalum is still subject to debate as the experimental results are controversial. The measured threshold from laser compressed tantalum single crystals is 35GP a, under which pressure the stress required for dislocation slip is lower than the twinning nucleation stress [37]. Meyers calculated the theoretical critical pressure for twinning in tantalum using a constitutive model [32], giving a pressure in the range 35 71GP a.…”

Surface topography evolution of Ni-based single crystal superalloy under laser shock: Formation of the nano-scale surface reliefs

“…between internal microstructures and mechanical performances [13][14][15][16]. For instance, microstructure characterization of monocrystalline copper subjected to laser-induced shock was investigated, and the results showed the evolution of defect structures.…”