Grain topology in Ti–6Al–4V welds—Monte Carlo simulation and experiments

Abstract

The importance of topological features of grains in the evolution of grain structure is well recognized in isothermal systems. However, during fusion welding, strong spatial gradients of temperature exist in the heat-affected zone (HAZ), and this region undergoes rapid heating and cooling. The effects of spatial and temporal variations of temperature on the topological class distribution, relationship between size and topology of grains and the interdependence between grain topology and its neighbours are not known. Topological features of grains in the HAZ of Ti-6Al-4V alloy welds were measured for various heat inputs in the range 0.55-4.33 MJ m −1. The topological class distributions were also calculated using a three-dimensional Monte Carlo model utilizing thermal cycles computed from a well tested numerical heat transfer and fluid flow model. The computed results showed that the topological class distributions were unaffected by the spatial and temporal variations of temperature. Experimental investigations of a few sections confirmed the simulation results. The average grain size for each edge class varied linearly with the edge class number. The local topological environment, i.e. the average number of sides of neighbours, n n , varied linearly with the inverse of the number of sides of grains, 1/n r , at a given location in the HAZ. Locations with the same topological environment showed the same grain size, indicating the significant influence of grain topology on grain growth in the HAZ.

Tailoring complex weld geometry through reliable heat-transfer and fluid-flow calculations and a genetic algorithm

“…Figure 3 shows the calculated enhancement factors for the thermal conductivity and viscosity as a function of heat input by using the vorticity-based turbulence model and the proposed Eqs. [13] and [14]. The calculated enhancement factors for thermal conductivity and viscosity by using vorticity-based turbulence also increase with an increase in the heat input per unit length as obtained by Eqs.…”

“…The calculated enhancement factors for thermal conductivity and viscosity by using vorticity-based turbulence also increase with an increase in the heat input per unit length as obtained by Eqs. [13] and [14]. The reasons for slightly lower values of the average enhancement factors for thermal conductivity and viscosity by the vorticitybased turbulence model compared to Eqs.…”

“…The reasons for slightly lower values of the average enhancement factors for thermal conductivity and viscosity by the vorticitybased turbulence model compared to Eqs. [13] and [14] are…”

“…These models have enabled accurate quantitative calculations of thermal cycles and fusion-zone geometry that have been used to quantitatively understand various attributes of the welded joints like weld metal-phase composition, [11,12] grain structure, [13,14] and inclusion structure. [15] Although these models have provided significant insight about the welding processes and welded materials, their applications have been limited due to several factors.…”

Predicting Mesoscale Microstructural Evolution in Electron Beam Welding

“…Significant advances were made by Debroy et al with a three-dimensional (3D) weld simulation. [12][13][14][15] Their studies demonstrated good agreement with experimental grain size distributions at various distances from the centerline of the FZ. Debroy and co-workers focused their analysis on the heat-affected zone (HAZ) surrounding the FZ and excluded the FZ from their simulation domain.…”