COMPUTATIONAL DESIGN OF COMPOSITIONALLY GRADED ALLOYS FOR PROPERTY MONOTONICITY

摘要

Compositionally graded alloys can realize multiple conflicting properties in the same part, but the formation of secondary phases can often lead to cracks or deleterious properties. In prior work, a computational methodology was presented that can design compositional gradients to avoid these phases at any temperature in high dimensions [1]. The methodology also optimizes paths for a specified cost function, but prior work only considered minimizing path length or maximizing obstacle clearance. In this work, a new cost function is presented to produce compositional paths with optimal property gradients. Specifically, monotonicity is presented as the optimal quality of a pathwise property gradient because monotonic property gradients can be transformed to nearly any form on the part by controlling deposition rate. The proposed cost function uses a metric for non-monotonicity to find the shortest path with monotonic properties and is shown to be compatible with optimal path planners. A synthetic case study examines the effect of a cost function parameter on the trade-off between length and monotonicity. The cost function is also demonstrated in the Fe-Co-Cr system to find a compositional path with monotonic gradients in Coefficient of Thermal Expansion (CTE). The deposition of the path on a hypothetical part is then planned subject to a maximum deposition rate and CTE gradient. Future work is proposed to extend the framework to optimize multiple properties at once and to incorporate Multi-Material Topology Optimization (MMTO) techniques into a complete design methodology for functionally graded metal parts.