The Effect of Stress State and Precipitation on Stress-Induced Martensitic Transformations in Polycrystalline and Single Crystal Shape Memory Alloys: Experiments and Micro-Mechanical Modeling

Gall, Kenneth Allen

Permalink

https://hdl.handle.net/2142/83968 Copy

Description

Title

The Effect of Stress State and Precipitation on Stress-Induced Martensitic Transformations in Polycrystalline and Single Crystal Shape Memory Alloys: Experiments and Micro-Mechanical Modeling

Author(s)

Gall, Kenneth Allen

Issue Date

1998

Doctoral Committee Chair(s)

Sehitoglu, Huseyin

Department of Study

Mechanical Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Engineering, Metallurgy

Language

eng

Abstract

To properly understand stress-induced transformations in aged NiTi single crystals, a micro-mechanical model is used to quantify the stress fields outside perfectly coherent Ti$\sb{11}$Ni$\sb{14}$ precipitates in NiTi. Using the model, the decrease in the orientation dependence of $\sigma\sb{\rm cr}$ is linked to the unique orientation relationship that exists between the coherent precipitates in NiTi and the martensite correspondence variant pairs. As experimentally observed the model predicts that peak aged NiTi single crystals loaded under tension along the (100) orientation will show a dramatic decrease in $\sigma\sb{\rm cr}$ while those loaded along (111) will show less of a decrease in $\sigma\sb{\rm cr}.$ The effect of different aging treatments is properly explained by extending the local stress field model to the case of semi-coherent precipitates. In addition, the depletion of Ni in the matrix surrounding the precipitates is found to contribute to changes in $\sigma\sb{\rm cr}$ and M$\sb{\rm s}$ for aged NiTi alloys.

Graduation Semester

1998

Type of Resource

text

Permalink

http://hdl.handle.net/2142/83968

Owning Collections