Effect Of Nb, Cr And W On The High Temperature Oxidation Behavior Of Ti-Al Alloys
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Date
2011-07
Authors
Sapiai, Napisah
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
This research is focused on intermetallic TiAl and their oxidation behavior for
structural materials at high temperatures in automotive, aerospace and gas turbine
industries. However, the commercial application of Ti-Al is currently limited by their
insufficient oxidation resistance at temperature above 700-850oC. The addition of
alloying elements such as Nb, Cr and W is significant in producing good Ti-Al alloys
for high temperature applications. Ti-Al alloys were fabricated using arc- melting
furnace. Then the phases present, microstructure evaluation and hardness test were
characterized using XRD, FESEM/EDX and Vikers hardness. After the analysis,
alloy samples were cut into size of 5x5x1 mm and then oxidized at 900oC for 10, 30,
50, 80, 100 and 200 hours. The weight gain was calculated in order to see the
oxidation rate. XRD result shows γ –TiAl and α-Ti3Al exists as major phases and β-Ti
and Al2Ti exists as a minor phases. The oxide scales formed is composed of outer
layer (consist of TiO2) intermediate layer (rich in Al2O3) and inner layers (consist of
TiO2 + Al2O3 mixed oxide with small amount of alloying element). The addition of (2
and 10 at.%) Nb in series 2 and (2 at.%) W in series 3 is effectively in increasing the
oxidation resistance. Meanwhile, addition of 4 at.% Cr (series 4) does not give
beneficial effect and it is harmful to substrate alloy. Addition of Nb and Cr together in
quaternary Ti-48Al-Nb-Cr (series 5) also not give significant effect to oxidation
resistance. The highest oxidation resistance is observed in series 6 (quaternary Ti-
48Al-Nb-W).
Description
Keywords
Intermetallic TiAl oxidation behavior for structural materials , at high temperatures in automotive