Strengthening of Alkali Halides by Divalent‐Ion Additions

Abstract

Single crystals of NaCl, NaBr, KCl, and KBr containing divalent additions of Ca2+, Sr2+, and Ba2+ were tested mechanically. In the solution‐treated condition, the yield strength, σv, as determined from compression testing in a 〈100〉 direction is essentially dependent on the concentration of the dopant only and is independent of the species of either the dopant or of the host material. All crystals soften on aging, with the exception of the NaCl:Ca2+, NaBr:Ca2+, and NaBr:Sr2+ systems. In addition, correlation was good between σv, and the Knoop hardness number, H, obtained by indentation with the long axis of the indenter aligned in 〈100〉. The equation is of the form σv=C(H–H0), where C≅ 0.21 for all four halide families and H0 is near the hardness value of the pure halides. Furthermore, H0≅5×10−3E111, the Young's modulus in the 〈111〉 direction. Hence σv≅0.21H–10−3E111.

Study on Dislocation-Dopant Ions Interaction in Ionic Crystals by the Strain-Rate Cycling Test during the Blaha Effect

“…This may be caused by the result that the separation between the weak obstacles lying on the mobile dislocation becomes wider as the I-V dipoles turn into aggregates. In addition, it is supposed that the decrease in τ p1 due to agglomerate of the I-V dipoles, i.e., softening, would be attributable to the loss of tetragonality (lattice distortion around the dopants) in terms of the Fleischer's model [74], as suggested by Chin et al [1]. The decrease in the effective stress due to agglomerates of I-V dipoles has been reported for alkali halide crystals doped with divalent cations so far [1,13,75,88,89].…”

“…This means that τ p1 and τ p2 increase, depending on the Sr 2+ concentration, because the yield stress generally increases with increasing impurity concentration [1][2][3]75,81]. The critical temperature (T c ), at which the T-τ p1 curves intersect the abscissa and τ p1 is zero, may be determined from Figure 11.…”

“…The interaction between a dislocation and point defects has been investigated by measurements of yield stress (e.g., [1][2][3][4][5][6][7]) and proof stress (e.g., [8,9]), micro-hardness tests (e.g., [10][11][12][13][14]), direct observations of dislocation (e.g., [15][16][17][18][19][20][21]), internal friction measurements (e.g., [22][23][24][25][26][27]), or stress relaxation tests (e.g., [28,29]) so far. A large number of investigations have been carried out by the separation of the flow stress into effective and internal stresses on the basis of the temperature dependence of yield stress, the strain rate dependence of flow stress, and the stress relaxation.…”

Mechanical and thermal properties of fine-grained quasi-eutectoid (La1−Yb )2Zr2O7 ceramics

“…Thus the higher hardness of Yb 2 Zr 2 O 7 may be due to smaller unit cell volume and smaller interatomic distance compared with La 2 Zr 2 O 7 . Generally speaking, the hardness of a solid solution usually exhibits a parabolic curve [38] with a positive deviation to linear blending line due to the "solid solution hardening" [34,39,40]. In the (La 1−x Yb x ) 2 Zr 2 O 7 system, the slight increase in hardness of the single phase (La 5/6 Yb 1/6 ) 2 Zr 2 O 7 and (La 1/6 Yb 5/6 ) 2 Zr 2 O 7 can be well explained by the solid solution hardening effect.…”

Investigation of the yield process by deformation luminescence of X-ray irradiated KCl:Ca2+

“…There are unresolved problems though the yield of materials is of practically importance. There is substantial literature reporting on the dependence of yield stress on temperature, solute concentration and heat treatment (Dryden, et al, 1965;Chin, et al, 1973). However, there is relatively less literature on the microscopic yield of crystals where dislocation starts to move and to multiply without returning to its original site, i.e.…”