Stress-induced phase transformations

V.V. Martynov, X-ray diffraction study of thermally and stress-induced phase transformations in single... 

A correlation between the total momentum of impinging ions per deposited boron atom and the c-BN deposition has been observed. In this model, c-BN formation is correlated with the momentum-drive process, such as the formation of point defects in conjunction with the stress-induced phase transformation. 

At the same time the phenomenon of fracture reflects, in one way or another, the ultimate limit of deformation in a solid. It thus involves fundamental physical properties of the material such as its inter-atomic bonding, its surface energy and its crystal structure. It also involves crystallographic processes such as slip, stress induced phase transformations and twinning, whilst in molecular solids such as polymers other processes such as molecular relaxation behaviour may predominate. Fracture is clearly of great scientific interest and has attracted the attention of chemists and solid state physicists as well as engineers. 

Stress-Induced Phase Transformation in Poly(vinylidene fluoride)... 

Budiansky B. and Truskinovsky L., On the Mechanics of Stress-Induced Phase Transformation in Zirconia, J. Mech. Phys. Solids 41, 1445 (1993). 

T.K. Gupta, F.F. Lange, and J.H. Bechtold, Effect of stress-induced phase transformation on the properties of polycrystalline zirconia containing metastable tetragonal phase, J. Mater. Sci. 13(7), 1464-1470 (1978). 

Several approaches have been taken to calculating the toughening associated with a stress-induced phase transformation and there is agreement between these various analyses. The simplest calculations assume the phase transformation is purely dilatational and that it is nucleated by a critical value of the mean stress at a crack tip. In a material that contains a crack, the transformation will occur in a frontal zone at the crack tip, as shown schematically in Fig. 8.60. For this case, the transformation is found not to increase toughness. Toughening only... 

Up to this point, it has been assumed that increasing zone size will be beneficial in terms of toughness. It must, however, be realized that there is a limiting zone size, above which the toughness must decrease. For example, if the critical transformation stress is reduced to a value such that the stress-induced phase transformation occurs throughout the specimen, the transformation zone will no longer be constrained. This implies that the zone will no longer be left in residual compression and the crack closure forces will vanish. The overall trend is shown schematically in Fig. 8.63. The stress required to induce the phase trans-... 

Figure 14.20 Microcrack process zone around a crack in an alumina-zirconia duplex ceramic, where the stress-induced phase transformation of zirconia particles induces microcracking. From Ref. [21],...

It is generally considered that dynamic fracture toughness is lower than static toughness in many metallic materials however, in the case of PSZ, the dynamic fracture toughness appears to be higher than the static. This is apparently related to the stress-induced phase transformation which occurs in PSZ. 

So-called stress-induced phase transformations can produce additional compressive residual stresses during crack propagation and thus increase the crack-growth resistance TTir. This is caused by particles in the matrix that can increase their volume by a phase transformation. Initially, the particles have to be in a metastable state which is thermodynamically unfavourable, but cannot transform to the thermodynamically stable phase because a nucleation barrier has to be overcome for this, similar to the process in precipitation hardening (see section 6.4.4). 

Fig. 7.7. Stress-strain diagram of a volume element, showing stress-induced phase transformations (after [46]). Similar to the formation of microcracks (figure 7.5), energy is dissipated during the loading and unloading cycle and thus increases the fracture toughness...

Transformation toughening increases the crack-growth resistance by producing compressive residual stresses in the material during crack propagation. These are caused by stress-induced phase transformations, described in section 7.2.4. To achieve this, particles are added to the matrix that perform a phase transformation that results in a larger volume of the particles when a sufficient tensile stress is applied. 

De Rosa C, Auriemma F (2011) Single site organometallic polymerization catalysis as a method to probe the properties of polyolefins. Polym Chem 2 2155-2168 De Rosa C, Auriemma F (2012) The deformability of polymers the role of disordered mesomorphic crystals and stress-induced phase transformations. Angew Chem Int Ed 51 1207-1211... 

An interesting role of dislocations is in the stress-induced phase transformation of orthoenstatite to clinoenstatite [317-319]. 

FR Chien, RJ Clifton, SR Nutt. Stress-induced phase transformation in single crystal titanium carbide. J Am Ceram Soc 78 1537, 1995. 

Schematic demonstration of transformation toughening. (a) A crack prior to inducement of the Zr02 particle phase transformation. b) Crack arrestment due to the stress-induced phase transformation.

Koi] Mechanical tests Stress-induced phase transformation and superplasticity... 

Koi] Koike, J., Shimoyama, Y, Ohnuma, L, Okamiua, T., Kainuma, R., Ishida, K., Maruyama,K., Stress-Induced Phase Transformation During Superplastic Deformation in Two-Phase Ti-Al-Fe , Acta Mater., 48, 2059-2069 (2000) (Calculation, Crys. Structiue, Phase Diagram, Phase Relations, Experimental, Thermodyn., 26)... 

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