Microstructural and mechanical properties of welded Ti-15-3 beta titanium alloy using GTAW with boron-modified fillers / Ahmad Lutfi Anis

Mechanical properties of titanium alloys are dictated by their microstructure, particularly the size, shape and distribution of hexagonally close-packed (hcp) α and body-centred cubic (bcc) β phases. For metastable β titanium alloys the morphology and distribution of α precipitates have largely cont...

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Main Author:	Anis, Ahmad Lutfi
Format:	Thesis
Language:	English
Published:	2017
Subjects:	Physical and theoretical chemistry
Online Access:	https://ir.uitm.edu.my/id/eprint/21619/1/TP_AHMAD%20LUTFI%20ANIS%20AP%2017_5.pdf
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spelling	my-uitm-ir.216192018-09-26T03:32:30Z Microstructural and mechanical properties of welded Ti-15-3 beta titanium alloy using GTAW with boron-modified fillers / Ahmad Lutfi Anis 2017 Anis, Ahmad Lutfi Physical and theoretical chemistry Mechanical properties of titanium alloys are dictated by their microstructure, particularly the size, shape and distribution of hexagonally close-packed (hcp) α and body-centred cubic (bcc) β phases. For metastable β titanium alloys the morphology and distribution of α precipitates have largely contributed to its mechanical properties. Welded zones in gas tungsten arc welding (GTAW) of metastable β titanium alloys exhibit retained β structure with inferior mechanical properties due to coarse columnar prior β grains and lack of α precipitates in the matrix in as-welded condition. In this work refinement of prior β grains and α. was achieved in GTAW welds of metastable β titanium alloy, Ti-15V-3Cr-3Al-3Sn (Ti-15-3) by current pulsing and modification of welding fillers. Autogenous pulsed current GTAW were performed at 0, 2, 4 and 6 Hz pulsing frequencies to determine optimum frequency for pulsed current welding of thin plates Ti-15-3 alloy. Welding of Ti-15-3 alloy using commercially pure α titanium (CPTi) alloy filler resulted in the precipitation of α phase from β phase during cooling to ambient temperature due to dilution of melted base metal with the filler metal. The GTAW welds with CP-Ti filler exhibit high hardness, higher tensile strength but lower % strain as compared to the autogenous weld owing to precipitation of a phase precipitation at β grain boundaries. Addition of 0.5 wt.% and 1.0 wt.% boron to CP-Ti fillers resulted in significantly refined fusion zone β grains in welds with CP-Ti-0.5B and CP-Ti-1 .0B fillers due to growth restriction mechanism associated with partitioning of boron during solidification. X-ray diffraction (XRD) analysis of autogenous welds showed only bcc β-Ti phase while indexed peaks for the weld samples with CP-Ti filler showed the presence of very small hcp α-Ti phase along with bcc β-Ti phase. Welds with CP-Ti-0.5B and CP-Ti-1.0B fillers showed additional orthorhombic TiB peaks. Mechanical tests show that hardness of the fusion zone and tensile strength in welds with boron-added CP-Ti fillers are higher than that in autogenous welds and welds with CP-Ti filler. Post-weld heat treatment (PWHT) of the welded samples increased α precipitation in all samples while FESEM and TEM analysis of the fusion zones showed α with higher aspect ratios in aged welds with boron-added CP-Ti fillers than autogenous weld and weld with CP-Ti filler, attributed to the additional nucleation sites provided by increase in boundary area of refined prior β grains with the addition of boron. PWHT weldments displayed higher hardness values, compared to similar regions in as-welded samples, and higher tensile strength after aging. 2017 Thesis https://ir.uitm.edu.my/id/eprint/21619/ https://ir.uitm.edu.my/id/eprint/21619/1/TP_AHMAD%20LUTFI%20ANIS%20AP%2017_5.pdf text en public phd doctoral Universiti Teknologi MARA Faculty of Applied Sciences
institution	Universiti Teknologi MARA
collection	UiTM Institutional Repository
language	English
topic	Physical and theoretical chemistry
spellingShingle	Physical and theoretical chemistry Anis, Ahmad Lutfi Microstructural and mechanical properties of welded Ti-15-3 beta titanium alloy using GTAW with boron-modified fillers / Ahmad Lutfi Anis
description	Mechanical properties of titanium alloys are dictated by their microstructure, particularly the size, shape and distribution of hexagonally close-packed (hcp) α and body-centred cubic (bcc) β phases. For metastable β titanium alloys the morphology and distribution of α precipitates have largely contributed to its mechanical properties. Welded zones in gas tungsten arc welding (GTAW) of metastable β titanium alloys exhibit retained β structure with inferior mechanical properties due to coarse columnar prior β grains and lack of α precipitates in the matrix in as-welded condition. In this work refinement of prior β grains and α. was achieved in GTAW welds of metastable β titanium alloy, Ti-15V-3Cr-3Al-3Sn (Ti-15-3) by current pulsing and modification of welding fillers. Autogenous pulsed current GTAW were performed at 0, 2, 4 and 6 Hz pulsing frequencies to determine optimum frequency for pulsed current welding of thin plates Ti-15-3 alloy. Welding of Ti-15-3 alloy using commercially pure α titanium (CPTi) alloy filler resulted in the precipitation of α phase from β phase during cooling to ambient temperature due to dilution of melted base metal with the filler metal. The GTAW welds with CP-Ti filler exhibit high hardness, higher tensile strength but lower % strain as compared to the autogenous weld owing to precipitation of a phase precipitation at β grain boundaries. Addition of 0.5 wt.% and 1.0 wt.% boron to CP-Ti fillers resulted in significantly refined fusion zone β grains in welds with CP-Ti-0.5B and CP-Ti-1 .0B fillers due to growth restriction mechanism associated with partitioning of boron during solidification. X-ray diffraction (XRD) analysis of autogenous welds showed only bcc β-Ti phase while indexed peaks for the weld samples with CP-Ti filler showed the presence of very small hcp α-Ti phase along with bcc β-Ti phase. Welds with CP-Ti-0.5B and CP-Ti-1.0B fillers showed additional orthorhombic TiB peaks. Mechanical tests show that hardness of the fusion zone and tensile strength in welds with boron-added CP-Ti fillers are higher than that in autogenous welds and welds with CP-Ti filler. Post-weld heat treatment (PWHT) of the welded samples increased α precipitation in all samples while FESEM and TEM analysis of the fusion zones showed α with higher aspect ratios in aged welds with boron-added CP-Ti fillers than autogenous weld and weld with CP-Ti filler, attributed to the additional nucleation sites provided by increase in boundary area of refined prior β grains with the addition of boron. PWHT weldments displayed higher hardness values, compared to similar regions in as-welded samples, and higher tensile strength after aging.
format	Thesis
qualification_name	Doctor of Philosophy (PhD.)
qualification_level	Doctorate
author	Anis, Ahmad Lutfi
author_facet	Anis, Ahmad Lutfi
author_sort	Anis, Ahmad Lutfi
title	Microstructural and mechanical properties of welded Ti-15-3 beta titanium alloy using GTAW with boron-modified fillers / Ahmad Lutfi Anis
title_short	Microstructural and mechanical properties of welded Ti-15-3 beta titanium alloy using GTAW with boron-modified fillers / Ahmad Lutfi Anis
title_full	Microstructural and mechanical properties of welded Ti-15-3 beta titanium alloy using GTAW with boron-modified fillers / Ahmad Lutfi Anis
title_fullStr	Microstructural and mechanical properties of welded Ti-15-3 beta titanium alloy using GTAW with boron-modified fillers / Ahmad Lutfi Anis
title_full_unstemmed	Microstructural and mechanical properties of welded Ti-15-3 beta titanium alloy using GTAW with boron-modified fillers / Ahmad Lutfi Anis
title_sort	microstructural and mechanical properties of welded ti-15-3 beta titanium alloy using gtaw with boron-modified fillers / ahmad lutfi anis
granting_institution	Universiti Teknologi MARA
granting_department	Faculty of Applied Sciences
publishDate	2017
url	https://ir.uitm.edu.my/id/eprint/21619/1/TP_AHMAD%20LUTFI%20ANIS%20AP%2017_5.pdf
_version_	1783733759048155136

Microstructural and mechanical properties of welded Ti-15-3 beta titanium alloy using GTAW with boron-modified fillers / Ahmad Lutfi Anis

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