Publications

Hot Isostatic Pressing (HIP) is investigated as a technique for joining the cermet WC-15% Co to itself. Encapsulation of the specimens prior to HIPing was carried out using steel encapsulation, glass encapsulation and self encapsulation. The bonds were evaluated using a four point bend method. It is shown that the glass and steel encapsulation methods have a number of inherent problems which make them inappropriate for near net shape processing. In contrast the novel self encapsulation method, described for the first time in this communication, is both simple and effective, producing joined material with bulk strength. The concept of self encapsulation is potentially widely applicable for joining composite materials.

The fundamental difficulties incorporating experimentally obtained-boundary disorientation distributions (BMD) into 3D microstructural models are discussed. An algorithm is described which overcomes these difficulties. The boundary misorientations are treated as a statistical ensemble which is evolved toward the desired BMD using a Monte Carlo method. The application of this algorithm to a number complex arbitrary BMDs shows that the approach is effective for both conserved and non-conserved textures. The algorithm is successfully used to create the BMDs observed in deformation microstructure containing both incidental dislocation boundaries (IDBs) and geometrically necessary boundaries (GNBs).

We propose a multi length scale approach to modeling recrystallization which links a dislocation model, a cell growth model and a macroscopic model. Although this methodology and linking framework will be applied to recrystallization, it is also applicable to other types of phase transformations in bulk and layered materials. Critical processes such as the dislocation structure evolution, nucleation, the evolution of crystal orientations into a preferred texture, and grain size evolution all operate at different length scales. In this paper we focus on incorporating experimental measurements of dislocation substructures, rnisorientation measurements of dislocation boundaries, and dislocation simulations into a mesoscopic model of cell growth. In particular, we show how feeding information from the dislocation model into the cell growth model can create realistic initial microstructure.

A novel Monte Carlo (MC) model of Zener pinning has been developed. It differs from previous MC models in that it does not simulate polycrystalline grain growth. Instead a single boundary moving through an array of particles is simulated. The boundary curvature defines the driving force acting on the boundary; this is constant throughout the simulation. By incrementally increasing the volume fraction of particles, the pinning force is gradually increased. The boundary is eventually pinned when driving force equals the pinning force. This defines the Zener criterion and enables the volume fraction dependence of the model to be determined. The value of this approach is that there is no limit imposed on either the volume fraction of particles or their size. Simulations have been carried out over a range of volume fractions, from 0 < f < 0.25 for particles with volumes of 27 sites. The pinning force exerted by particles on a boundary is related to the characteristic shape during bypass, the so called dimple. When the simulation temperature is T{prime} = 0, dimples are not formed, the boundaries experience an artificially strong pinning force and the model exhibits an f{sup {minus}1/2} dependence. When T{prime} is greater than a critical value dimples are formed and the model shows an f{sup {minus}1} volume fraction dependence. The implications of this result for previously MC models of Zener pinning is discussed.