Nanocrystalline (nc) Al-Pb two phase mixtures of different Pb concentrations were made by two different routes using high energy ball milling. The microhardness measurements show a softening in nc Al-Pb composites with the increase in Pb content, contradicting the previous results reported in the literature. We conclude that interaction of Pb atoms with nanocrystalline Al grain boundaries is responsible for the softening of the nc Al matrix observed in the current study. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
This work gives an overview of the theoretical background and of the numerical modelling framework used to describe the mechanical properties and the response of materials on scales ranging from the atomistic, through the microstructure and all the way up to the macroscale. In order to describe the dual nature of the structure of matter, which is continuous when viewed at large length scales and discrete when viewed at the atomic scale, plus the interdependence of these scales, multiscale modelling is required to complement the continuum and the atomistic models. More specifically, what we aim for in this review is to present and discuss the following basic conceptual models, as well as the methodologies that accompany them: (a) discrete models such as ab initio, atomistic / molecular, mesoscopic; (b) continuum mechanics models (CMM) comprising pure CMM, non-local elasticity CMM, higher-order strain gradient and higher-order nonlocal strain gradient elasticity CMM, and surface elasticity CMM; (c) multiscale material models (MMM). Since the field of nanomechanics is currently a rapidly expanding research area, the presented state-of-the art is by no means exhaustive. It simply outlines the research efforts that go behind formulating numerical models for the solution of problems in nanomechanics. Despite the advantages that boundary element methods (BEM) have in solving problems at the physical scale, either as stand-alone or in combination with finite element methods (FEM), their application to multiscale modelling is still limited, despite the promise they seem to hold.
17-4 PH stainless steel and Al2O3 ceramic were successfully vacuum brazed using graphene reinforced Ag-Cu-Ti brazing alloy. In this paper, the effects of operating parameter such as brazing temperature, holding time and graphene amount on the microstructure and mechanical properties of the brazed joints were systematically studied. The experiment revealed that with the elevation of brazing temperature and holding time, the shear strength of 17-4 PH stainless steel and Al2O3 ceramic joints brazed with Ag-Cu-Ti filler alloy increased first, getting the maximum 170 MPa at 880 °C for 10 min and then declined. When the joint brazed with 0.1 wt % graphene reinforced Ag-Cu-Ti composite filler, the maximum shear strength reached 212 MPa that was 25% higher than the joint with single Ag-Cu-Ti filler metal. Moreover, fracture path of the 17-4 PH stainless steel and Al2O3 ceramic joint with 0.1 wt % graphene reinforced Ag-Cu-Ti was changed from the ceramic to the reaction layer that was closed to Al2O3 substrate. The improvement of the joint shear strength was chiefly benefited from the formation of TiC particle that reinforced brazing seam and the refinement of joint microstructure.
Interdiffusion in single-phase diffusion couples of TiAl and Ti3Al has been investigated over the temperature range of 1118 to 1583 K. Concentration distributions after annealing were measured by an electron probe microanalyzer (EPMA). Interdiffusion coefficients were calculated according to the Boltzmann-Matano method. No significant concentration dependence of the interdiffusivities in both compounds was detected. The temperature dependence of the diffusivities follows Arrhenius laws with a pre-exponential factor D0 = 2.8 × 10−4 m2 s−1 and an activation enthalpy Q = (295 ± 10) kJ mol−1 for TiAl, and D0 = 1 × 10−3 m2 s−1 and Q = (312 ± 6) kJ mol−1 for Ti3Al, respectively. The present results are discussed together with Ti self-diffusion data for TiAl and Ti3Al from tracer-diffusion experiments.
Solid state actuation characteristics of CuAlMn shape memory alloys (SMAs) are reported at extreme low temperatures (
