## Electronic Theses and Dissertations

1993

Thesis

M.A.Sc.

#### Department

Mechanical, Automotive, and Materials Engineering

Youdelis, W. V.,

#### Keywords

Engineering, Materials Science.

CC BY-NC-ND 4.0

#### Abstract

The effects of Be and Ti microadditions on the transformation of tempered martensite aluminum bronze are investigated. The alloys investigated are the base alloy of nominal composition Cu-11Al, and the base alloy containing 0.20Be, 0.20Ti, and 0.20Be + 0.20Ti. Two hardness peaks are identified in the base alloy and base alloy containing 0.20Be, and one hardness peak in the base alloys containing 0.20Ti and 0.20Be + 0.20Ti, for aging between 400$\sp\circ$C and 500$\sp\circ$C following a solution treatment at 950$\sp\circ$C. A second minor increase in hardness results in the base alloy and base alloy containing 0.20Be, which is attributed to $\gamma\sb1$ phase formation in the eutectoid (pearlite) reaction. By monitoring microhardness and resistivity changes, coupled with optical microscopical observations, it is shown that microadditions of both Be and Ti, and more so with the Be + Ti combination, significantly accelerates the precipitation kinetics, and increases the initial peak microhardness of the alloys following a solution and aging treatment between 400$\sp\circ$C-500$\sp\circ$C. A thermodynamic analysis of precipitate formation suggests that the increased transformation rate could be accounted for by a Be and Ti enhanced nucleation rate, in particular by the formation of the heterogeneous substrate TiBe$\sb{12}$ in the base alloy containing 0.20Be + 0.20Ti. The increased transformation rate for the microalloyed alloys is evident in the microstructures of both the aged and slowly cooled alloys. The annealed and slowly cooled alloys show more decomposition product $(\alpha)$ in the structures of the microalloyed alloys, and an earlier and finer eutectoid (pearlite) structure in the aged alloys containing the Be and Ti microadditions. (Abstract shortened by UMI.) Source: Masters Abstracts International, Volume: 32-02, page: 0700. Adviser: W. V. Youdelis. Thesis (M.A.Sc.)--University of Windsor (Canada), 1993.

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