Beta titanium (β-Ti) alloys have been a subject area of intense interest since 1980s. By virtue of their unique properties, β-Ti alloys very well compliment the alpha and alpha + beta alloys. Heat treatment of β-Ti alloys is the crux to their technology and application. Over the last two decades, a number of researches have been carried out on issues related to heat treatment of these alloys—sub-transus solution treatment, duplex aging and heating rate to aging temperature. Improved understanding resulting from these studies has enabled designing optimum heat treatments to achieve refined microstructures free from deleterious features with improved mechanical properties under static and dynamic loading conditions. The purpose of this overview is to take stock of progress made in recent years in understanding the heat treatment of β-Ti alloys for a better commercial exploitation. © 2016, The Indian Institute of Metals - IIM.

Geetha M

Department of Control and Automation

School of Electrical Engineering

Vellore Campus

Nageswara Rao M

Department of Manufacturing Engineering

School of Mechanical Engineering

Santhosh R

Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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Transactions of the Indian Institute of Metals

The paper presents a study of the surface and subsurface characteristics induced by laser peening without coating (LPwC) and dual shot peening (DSP) on the duplex aged Ti-15 V-3Al-3Cr-3Sn alloy. In 3D-optical topography analysis, DSP resulted in a six-fold enhancement in the surface roughness (Sa). Whereas, LPwC resulted in unaltered surface roughness (Sa) compared to the polished/unpeened sample. In cross-sectional microstructure studies, deformed grains and heat affected zones were observed in the near surface region of shot peened, and laser peened samples respectively. Moreover, compared to bulk hardness, shot peening and laser peening has resulted in maximum increment of ~28% and ~12% in microhardness of the near peened surface region respectively. © 2020, Springer Nature Singapore Pte Ltd.

Lecture Notes in Mechanical Engineering Advanced Surface Enhancement

A Comparison of Surface and Sub-surface Features Induced by Shot Peening vs. Laser Peening on a Duplex Aged Beta Ti Alloy

In the present study, Ti-15V-3Al-3Cr-3Sn (Ti-15-3), a beta titanium aerospace alloy in solution treated condition (850 °C/1 h) was subjected to Laser Peening without Coating (LPwC) with a wavelength of 532 nm and power density of 8.96 GW cm−2. Surface roughness was analysed using 3D optical topography. Curiously, in the near peened surface, peening induced precipitation (i.e. 19% of α precipitation) and increased fraction of low angle boundaries (∼123%) was revealed through the Electron Back Scattered Diffraction (EBSD) analysis. Through depth nanohardness measurement was carried out along the cross-section of the peened sample right from the near peened surface. Peak hardness of 4.6 GPa is observed at a depth of 100 µm from the peened surface while the base/bulk hardness of the material is 4 GPa. In addition, X-Ray Diffraction (XRD) based analysis confirmed the presence of compressive residual stress in the near surface region of the peened sample. To understand the effect of the peening induced microstructural changes and residual stresses in fatigue behaviour, staircase method of fatigue analysis was adopted and observed that the more number of run out samples belonged to laser peened condition when compared to the unpeened condition. Despite this favourable indication, fatigue limit remains more or less unaltered even after peening. Fractography studies revealed the least influence of the surface roughness induced by laser peening over the crack initiation. Irrespective of the condition (i.e. unpeened and laser peened), crack initiation was predominantly influenced by the stress concentration co-existing at the sharp corners. © 2018 Elsevier Ltd

Optics & Laser Technology

Influence of laser peening without coating on microstructure and fatigue limit of Ti-15V-3Al-3Cr-3Sn

Fulltext

Titanium Alloys - Novel Aspects of Their Processing [Working Title]

Processing of Beta Titanium Alloys for Aerospace and Biomedical Applications

Beta titanium (β-Ti) alloys have emerged over the last 3 to 4 decades as an important class of titanium alloys. Many of the applications that they found, particularly in aerospace sector, are such that their high cycle fatigue (HCF) behavior becomes critical. In HCF regime, crack nucleation accounts for major part of the life. Consequently it becomes important to understand the mechanisms underlying the nucleation of cracks under HCF type loading conditions. The purpose of this review is to document the best understanding we have on date on crack nucleation in β-Ti alloys under HCF conditions. Role of various microstructural features encountered in β-Ti alloys in influencing the crack nucleation under HCF conditions has been reviewed. It has been brought out that changes in processing can result in changes in microstructure which in turn influence the time for crack nucleation/fatigue life and fatigue limit. While majority of fatigue failures originate at the surface, subsurface cracking is not uncommon with β-Ti alloys and the factors leading to subsurface cracking have been discussed in this review. © Published under licence by IOP Publishing Ltd.

Journal of Physics: Conference Series

Crack Nucleation inβTitanium Alloys under High Cycle Fatigue Conditions - A Review

The microstructure and mechanical behavior of beta titanium alloy Ti-15V-3Cr-3Al-3Sn (Ti15-3) under unidirectional and high cycle fatigue (HCF) loading conditions were studied after single aging (SA) and duplex aging (DA). After SA, well-developed grain boundary α and micro precipitate free zones (micro PFZs) were present in the microstructure. Whereas after DA, grain boundary α was poorly developed and micro PFZs were absent. DA resulted in smaller size, higher density and volume fraction of alpha particles. DA led to higher work hardening rate, better strength-ductility combination and higher HCF life. Improved mechanical behavior after DA is explained based on microstructural observations. © 2014 Elsevier Ltd. All rights reserved.

International Journal of Fatigue

Effect of duplex aging on microstructure and mechanical behavior of beta titanium alloy Ti–15V–3Cr–3Al–3Sn under unidirectional and cyclic loading conditions

The kinetics of the β → α + β phase transformation in Ti-15V-3Cr-3Al-3Sn (Ti15-3) alloy was studied at 500 °C. A method is proposed and used to estimate the volume fraction of α phase as a function of aging time based on X-ray diffraction (XRD). The method uses the results of calculations of phase equilibria at 500 °C performed using Thermo-Calc. The present work also reports results of calculations of phase equilibria over the temperature range 200-600 °C. In order to validate XRD based approach, select measurements of the quantity of α phase precipitation were done by the use of Field Emission Scanning Electron Microscopy. Results obtained were in reasonable agreement with those obtained using XRD. The kinetics of the β → α + β phase transformation was modelled in the theoretical framework of the Johnson-Mehl-Avrami (JMA) theory and a mechanism based on slow diffusion controlled growth of very fine α plates is proposed. Using the derived JMA kinetic parameters, fraction of transformed α was calculated as a function of aging time; the calculated and experimentally measured values were found to be in good agreement. © 2014 Elsevier B.V. All rights reserved.

Journal of Alloys and Compounds

Experimental study and computer modelling of the β → α + β phase transformation in Ti15-3 alloy under isothermal conditions

A comparison between slow heating to aging temperature and direct charging at aging temperature on the microstructure and mechanical properties obtained after the aging was established for the metastable beta (β) titanium alloy Ti-15V-3Cr-3Al-3Sn. The alloy was subjected to two single aging (SA) and two duplex aging (DA) conditions, with two heating rates to aging temperature: (i) low heating rate of 5 oC/min (ii) direct charging into a furnace heated to aging temperature. The microstructure analysis was carried out using Field Emission Scanning Electron Microscopy. Mechanical Testing was carried to evaluate Ultimate Tensile Strength (UTS), 0.2% Yield Strength (YS), % Elongation (%El.), % Reduction in area (%RA) and hardness. In the case of SA samples aged at 500 °C for 8 h and 500 °C for 10 h, heating rate of 5 °C/min to aging temperature resulted in a finer microstructure but did not help in achieving better strength-ductility combination compared to direct charging. Lower rate of heating allows enough dwell time in the temperature range 250-300 oC for pre-precipitation reaction to occur which aids in fine scale precipitation of alpha phase during aging. In the case of DA samples aged at 250 oC for 24 h followed by 500 oC for 8 h and 300 oC for 10 h followed by 500 oC for 10 h, no tangible difference between lower rate of heating and direct charging was observed in mechanical properties or microstructure. This is believed to be due to the pre-aging steps 250 oC/24 h or 300 oC/10h in the two DA treatments, which create finely distributed precursors thereby leaving no scope for the heating rate to play a role.

Advanced Materials Research

Influence of Rate of Heating to Aging Temperature on Precipitation Hardening in a Metastable β Titanium Alloy

This paper presents the age hardening behavior of metastable beta titanium alloy Ti-15 V-3Cr-3Al-3Sn subjected to various single and duplex aging treatments. Single aging was carried out in the range 200-550 °C for times up to 150 h (h). For duplex aging first step was performed in two different ways: (i) 250 °C for 24 h (ii) 300 °C for 10 h; second step was carried in the range 350-500 °C, for times up to 150 h. The decomposition of alpha (α) phase during aging was monitored by hardness measurements, tensile testing, different microscopic techniques and X-ray diffraction. Duplex aging treatments resulted in higher hardness and strength compared to single aging. There was a good balance of tensile strength and ductility after two duplex aging treatments 300 °C/10 h + 500 °C/10 h and 250 °C/24 h + 500 °C/8 h. Precipitate free zones (PFZs) were observed when aged at ≤450 °C in the microstructure; aging at ≥500 °C gave freedom from such zones. Duplex aging resulted in a finer size and higher density of α precipitates compared to single aging. Duplex aging 250 °C/24 h + 500 °C/8 h led to a four to five fold improvement in high cycle fatigue (HCF) life compared to single aging at 500 °C/10 h. The observed improvement in HCF life could thus be related to smaller size and larger density of α precipitates resulting from duplex aging. Optical microscopy and X-ray diffraction studies clearly revealed that preaging for 10 h at 300 °C accelerated the α-phase precipitation reaction during aging. © 2014 Elsevier B.V. All rights reserved.

Journal	Data powered by TypesetTransactions of the Indian Institute of Metals
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ISSN	0972-2815
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