Effects of hydrostatic pressure on mechanical behaviour and deformation processing of materials

Effects of Test Temperature and Loading Conditions on the Tensile Properties of a Zr-Based Bulk Metallic Glass

“…The stress state is a combination of tensile and hydrostatic stresses, as opposed to the compressive and hydrostatic stress state induced by the hardness tests. [47] It should be clear that while hot microhardness testing provides a reasonable estimate of strength, the strength values estimated from microhardness tests are consistently lower at given test temperatures than those presently measured from tensile tests. In these cases, the difference in values cannot be normalized by the proportionality constant, since the microhardness tests and tensile tests each induce different deformation mechanisms, and they compete differently with increasing temperatures, as described earlier.…”

Effects of Annealing and Pressure on Devitrification and Mechanical Properties of Amorphous Al87Ni7Gd6

“…The former is deformed under conditions of compression plus high superimposed compression, while the latter is deformed under conditions of tension plus some level of hydrostatic tension. [16] Slight irregularities and scratches on the ribbon surfaces may significantly affect the initiation of fracture in the tension test, while not significantly affecting that of the hardness. It is also possible that the solute enrichment of the remaining matrix occurs to such an extent as to embrittle the ribbon when tested in tension but not under indentation, as discussed previously and reviewed by others.…”

“…Ribbon materials were stored under refrigeration to minimize diffusion-related changes at room temperature, while characterization by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM) was performed, as described by Ko et al [3] Isothermal annealing treatments were conducted on 30-to 40-mm-long individual specimens for 30 minutes in silicone oil (GE, USEP SF 1147) maintained at 123°C, 145°C, 158°C, 173°C, 188°C, 191°C, 205°C, 232°C, and 262°C in an Innovare hydrostatic extrusion rig. [16] Additional isothermal annealing experiments were conducted at 123°C, 145°C, 158°C, 173°C, 188°C, 191°C, 205°C, and 232°C in oil, which was maintained at 940 MPa superimposed pressure in the Innovare hydrostatic extrusion rig. Experimental details are described by Wesseling et al [13] The total time at temperature was constant for both the atmospheric pressure and high pressure tests.…”

Stress-State Effects on the Fracture of a Zr-Ti-Ni-Cu-Be Bulk Amorphous Alloy

“…Confined pressure experiments are one means to directly determine the flow and fracture behavior under different stress states. Experiments on crystalline metals were performed as early as 1911 by Bridgman [8] and Von Karman [9] and reviewed recently by Lewandowski et al [10] Cubic crystalline metals and alloys have been documented to exhibit minimal pressure/normal stress dependence of the flow, [10] although the slight positive pressure dependence to the flow of both crystalline Al and Fe based systems was related to the slight positive pressure dependence of the shear modulus [11] in those materials. Fe, [12] Cr, [13] and NiAl [14][15][16] have also been shown to exhibit a negative dependence of the yield stress with increasing pressure due to the pressureinduced generation of mobile dislocations at inclusions in materials (e.g., Fe, Cr, and NiAl) that exhibit a sharp yield point due to dislocations previously pinned by interstitial atoms (e.g., C and N).…”

“…Fe, [12] Cr, [13] and NiAl [14][15][16] have also been shown to exhibit a negative dependence of the yield stress with increasing pressure due to the pressureinduced generation of mobile dislocations at inclusions in materials (e.g., Fe, Cr, and NiAl) that exhibit a sharp yield point due to dislocations previously pinned by interstitial atoms (e.g., C and N). Noncubic crystalline metals can also exhibit significant positive pressure dependence to the flow as reviewed elsewhere, [10] while metallic composite materials generally also show this behavior [17][18][19] due to the pressure-induced suppression of damage (e.g., reinforcement cracking, interfacial separation, and matrix failure).…”