Influence of niobium and yttrium on plastic deformation energy and plasticity of Ti-based amorphous alloys

Many amorphous alloys have been developed to date,but the low plasticity has limited their application.To achieve an amorphous alloy with high plasticity,a series of(Ti_(40)Zr_(25)Cu_(9)Ni_(8) Be_(18))_(100-x)TM_(x)(x=0,1,2,3,4 at.%,TM=Nb,Y)alloys were designed to study the influence of Nb and Y addition on the plasticity.The amorphous samples were prepared using the vacuum melting and copper mold casting process.The microstructures,glass forming ability and mechanical properties of the alloys were investigated by X-ray diffractometry(XRD),scanning electron microscopy(SEM),high-resolution transmission electron microscopy(HRTEM),depth-sensitive nanoindentation,and uniaxial compressive test.The plasticity of different bulk amorphous alloys was investigated by measuring the plastic deformation energy(PDE)during loading.The relationship between the PDE value and plasticity in bulk amorphous alloys was explored.Results show that Nb addition decreases the PDE value and promotes the generation of multiple shear bands,which significantly increases the fracture strength and plasticity,while the addition of Y element reduces the fracture strength and plastic strain of the alloy.

Measurement of the Energy Absorbed during Nanoscale Deformation of Human Peritubular and Intertubular Dentin

Mineralized tissues are usually constructed of nanosized materials with ordered hierarchical structures. The main reason for their high load-bearing ability is the multi-scale hierarchy. It is important to have a method for measuring the energy absorbed during the nanoscale deformation of mineralized tissues. The objective of this study was to use a combination of nanoindentation and elastic-plastic mechanics techniques to measure the damage resistance of peritubular and intertubular dentin, based on the energy consumed in the plastic deformation regime and the volume created by the indents. The control materials were soda-lime glass, gold, and poly-methyl methacrylate (PMMA). Plastic deformation energy was calculated from the plastic part of load-displacement curves. The mean values of peritubular dentin and intertubular dentin were 3.8 × 109, and 5.2 × 109 J/m3, respectively, compared to glass, PMMA, and gold which were 3.3 × 107, 1.3 × 109, and 3.1 × 109 J/m3, respectively. This method can be applied to study the resistance of mineralized tissues or organic/inorganic hybrid materials to deformation at the nanoscale.

Energy dissipation and contour integral characterizing fracture behavior of incremental plasticity

J ep -integral is derived for characterizing the frac- ture behavior of elastic-plastic materials. The J ep -integral differs from Rice’s J-integral in that the free energy density rather than the stress working density is employed to define energy-momentum tensor. The J ep -integral is proved to be path-dependent regardless of incremental plasticity and deformation plasticity. The J epintegral possesses clearly clear physical meaning： （1） the value J ep tip evaluated on the infinitely small contour surrounding the crack tip represents the crack tip energy dissipation; （2） when the global steadystate crack growth condition is approached, the value of J ep farss calculated along the boundary contour equals to the sum of crack tip dissipation and bulk dissipation of plastic zone. The theoretical results are verified by simulating mode I crack problems.

Deformation behavior of Fe-Mn-C TWIP steel within the temperature range of hot rolling

The hot-deformation behavior of Fe-Mn-C twinning induced plasticity （TWIP） steel was investigated by conducting hot compression tests within a recommended hot rolling temperature range at various strain rates. Flow resistance curves during hot-deformation were obtained, and strain rate sensitivities and activation energies for plastic deformation were calculated using the power law. It is found that the addition of Al and Si clearly increases the peak stresses for the present alloys, especially at 950℃. But Mn has a minor effect on the stress-strain curves and activation energy when its content varies from 15 mass% to 22 mass% for the present alloys.