Creep Strain Behaviors of Ti-6Al-4V Using Gleeble 3500

Abstract

During forging operations, strain can occur through three primary mechanisms: strain due to load applied through dies, strain due to thermal contraction, and strain due to creep. In materials behavior models, strain due to applied load and thermal contraction are directly considered and predictions are based on thermophysical properties and flow stress behaviors as inputs to the models. Strain due to creep after forging (during cooling) is often more difficult to predict and capture due to lack of materials data. In particular, data that capture the changing flow stress behavior during cooling (rather than from isothermal testing) are not commonly available. In this project, creep strain behavior during cooling was investigated by physical simulations using a Gleeble 3500. Standard cylinder-shaped Ti-6Al-4V samples with 10 mm diameter were heated to below β-transus temperature (1775°F) or above β-transus (1925°F), followed by constant cooling rates of 250°F/min and 1000°F/min with and without applied load during cooling to 1000°F. Total strain for the tests ranged from 2 – 6%. Characterization of prior microstructure and texture was carried out using XRD, optical microscopy, and SEM. The results provide insights on the relationship of flow stress behavior and microstructure as a function of temperature and cooling rate and are applicable to forging practices. These materials data can be used as input for future process modeling, potentially giving better prediction accuracy in industry applications.

Development and industrial application of integrated computational materials engineering

“…Extrapolation of thermophysical and mechanical data to elevated temperatures or processing conditions are often not appropriate and introduce errors and uncertainty into final component predictions. There have been various efforts aimed at the development of non-standard and transient thermophysical and mechanical property data through unique measurement and analysis methods (Shen 1992, Zhang 2021. Specific heat, viscosity and surface tension for in-process liquid material have been investigated through containerless processing under micro-gravity conditions (Mohr 2019).…”

“…These efforts have provided accurate and appropriate properties, but these types of physical tests and measurements are not readily accessible to industry, but they can be used to validate first-principles models that can be further used by industry to predict difficult to measure liquid properties (Woodward 2008, Woodward 2012. Collaborative efforts to establish manufacturing relevant materials data by both the development of advanced physical testing methods and data analytics have supported industrial implementation of ICME tools and methods (Semiatin 2015, Zhang et al 2021. Materials property data required for manufacturing process simulation is a technology area of opportunity for further improvement through the potential development of industry standard measurement and analysis methods, and through validated first principles calculations.…”