Influence of tempering temperature and time on the α′-Ti-6Al-4V martensite

doi:10.1016/0925-8388(95)02057-8

Journal of Alloys and Compounds

Volume 234, Issue 2, 15 February 1996, Pages 287-289

https://doi.org/10.1016/0925-8388(95)02057-8 Get rights and content

Abstract

The decomposition of α′ martensite of Ti-6Al-4V by tempering has been studied. The α′ martensite transforms during tempering heat treatment, decomposing to α and β phases. Different degrees of α′ decomposition, depending on temperature and heating time, have been observed. At low annealing temperatures the decomposition is incomplete, as is shown by the low value of the hardness. At temperatures above M_f the decomposition of α′ reaches completion. The microstructures have been observed by means of scanning electron microscopy.

References (6)

F.J. Gil et al.
Scr. Metall. Mater.
(1991)
I.J. Polmear
Light Alloys, Metallurgy of the Light Alloys
(1984)
J.C. Williams et al.
Titanium Technology

There are more references available in the full text version of this article.

Cited by (193)

Hydrogen promoted Ti<inf>3</inf>Al precipitation during Ti-6Al-4V martensite tempering
2024, Materials Today Communications
Temporary hydrogen alloying (THA) treatments are extensively used to refine coarse Ti-6Al-4V microstructures. The present study focuses on a THA treatment which promotes martensite decomposition; it highlights the effect of hydrogen on tempered martensite evolution by comparing martensite decomposition in hydrogenated and control samples. Microstructure evolution was characterised using X-ray diffraction (XRD), electron backscatter diffraction (EBSD), transmission Kikuchi diffraction (TKD), high-resolution transmission electron microscopy (HRTEM) and energy dispersive spectroscopy (EDS). Bulk XRD measurements indicate that quenching hydrogenated Ti-6Al-4V from the beta region causes a partial beta to hexagonal (α’) plus orthorhombic (α’’) martensite transformation. The EBSD, TKD and HRTEM analyses show that hydrogen saturated plate martensite decomposes to form a nanobanded structure which consists of nanosized, periodical Al-rich, and V-rich HCP regions that stabilise D0₁₉ Ti₃Al within 3 h of tempering. In comparison, typical martensite decomposition is observed in the control experiment. Quenching non-hydrogenated Ti-6Al-4V from the beta region causes a full beta to hexagonal (α’) martensite transformation. Elemental partitioning occurs, but not to the extent that D0₁₉ Ti₃Al is promoted and compositional banding is not observed. Formation of the nanobanded structure suggests that hydrogen altered the transformation pathway in hydrogenated martensite because of the presence of α’’possibly promoting spinodal decomposition.
Understanding the role of geometry and interlayer cooling time on microstructure variations in LPBF Ti6Al4V through part-scale scan-resolved thermal modeling
2024, Additive Manufacturing Letters
In this study, we investigated the microstructural variation of Ti-6Al-4 V in inverted pyramid parts built using Laser Powder Bed Fusion (LPBF). Two parts were fabricated with and without ghost parts to study the effects of interlayer delay time on thermal history and microstructure. Finite Element Method (FEM) based process simulation was used to predict the thermal history and cooling rates during the LPBF process to understand the location-specific microstructure and mechanical properties variation. The thermal analysis findings revealed that the variations in the cooling rates and pre-deposition temperature were notably significant. Within the same part, the cooling rates exhibited significant variations, differing by up to three orders of magnitude in two scenarios: (1) within the same layer, influenced by the proximity to the edges, and (2) at different heights, attributable to the strongly varying cross-section. Comparing the two parts, the cooling rates of the part with ghost parts were approximately two orders of magnitude higher than in the part without the ghost parts. This significant difference can be attributed to the extended interlayer cooling time and lower pre-deposition temperature resulting from the presence of two ghost parts which introduced an effective delay time between laser scans. Experimental validation against microstructure images and hardness measurements showed similar trends with the predicted results. These findings provide valuable insights into controlling microstructure at specific locations during LPBF fabrication, which is essential for building complex geometries with controlled material properties.
Effects of oxygen on microstructure and mechanical properties of selective laser melted Ti–6Al–4V annealed at different temperatures
2024, Materials Science and Engineering: A
For SLMed Ti–6Al–4V-xO (x = 0.11, 0.16, 0.21, and 0.25 wt%) alloys, both microstructure and mechanical properties are sensitive to oxygen content. The α′ martensites in as-built state transform to a ‘bimodal’ microstructure containing α lamellae interspersed with β transformed regions after 2 h annealing at 800 °C, 850 °C, 900 °C, and 950 °C followed by air cooling. The α lamellar width decreases and the β phase volume fraction increases with increasing oxygen content, due to reduced diffusivity of Al and V. The solid solution hardening effect of oxygen was quantified as: $σ_{0} = 472 MPa + 2159 c^{0.5}$ , where $σ_{0}$ is the lattice frictional stress and c is oxygen atomic fraction of the alloy. Increased oxygen content causes reduced fracture toughness and higher fatigue crack growth rate in the unstable growth regime, and the appearance of bilinear growth rate of the Paris regime at high annealing temperatures. The absence of the bilinear behaviour in the low oxygen content alloy and for annealing at low temperatures was interpreted in terms of changes in microstructural characteristics caused by oxygen impeding the diffusion of Al and V.
Experimental-numerical Investigation of ⍺/β-phase formation within thin electron beam melted Ti–6Al–4V
2024, Heliyon
Electron beam melting is a powder bed fusion process capable of manufacturing thin structural features. However, as the thickness of these features approaches typical microstructure grain sizes, it becomes vital to understand how the manufacturing process contributes to local crystallographic texture and anisotropy in micromechanical response. Therefore, this article investigates Ti–6Al–4V ⍺/β-phase formation within thin components using a variety of experimental and numerical approaches. Optical and scanning electron microscopy are used to determine through-thickness distributions of prior-β width ([top, middle, bottom]:[81.2 ± 44.2, 76.02 ± 30.4, 75.6 ± 31.2] μm), ⍺-lath thickness ([top, middle, bottom]:[1.0 ± 1.3, 1.3 ± 1.2, 1.4 ± 1.8] μm; average), and ⍺/β-phase fractions ([top, middle, bottom]:[0.87 ± 0.05, 0.82 ± 0.03, 0.88 ± 0.03]; average). Manufacturing process (i.e., “logfile”) data is used within a layer-by-layer finite element “birth/death” model. This model is loosely coupled with the Kim-Kim-Suzuki phase field model and a CALPHAD thermodynamic database to predict ⍺-lath growth throughout the process. In general, good correlation is found between the experimental data and the predicted temperature history, ⍺-lath coarsening, and phase fraction. This indicates that these tools would be useful in predicting process-structure-properties-performance relationships for thin features.
Microstructure and defect sensitivities in the very high-cycle fatigue response of Laser Powder Bed Fused Ti–6Al–4V
2023, International Journal of Fatigue
This work aims to analyze the sensitivity of the very high-cycle fatigue behavior of LPBF-Ti-6Al-4V to microstructure and porosity variations. To do so ultrasonic fatigue testing is performed on five grades of LPBF-Ti-6Al-4V. These grades were generated using different LPBF process parameters and different thermal post-treatments allowing to separately investigate the sensitivity to microstructure and porosity variations. It was found that both material features highly influenced the VHCF properties of LPBF-Ti-6Al-4V revealing the sensitivity to these features. Furthermore, the largest defect (pore or grain) controls fatigue crack initiation.
A study of microstructural factors governing strength and ductility of titanium alloys fabricated by powder bed fusion additive manufacturing
2023, Journal of Alloys and Compounds
This work aims to reveal the general patterns of the strength and ductility of titanium alloys fabricated by using powder bed fusion (PBF) additive manufacturing (AM). The dislocation-based constitutive modeling and reported experimental data are coupled for a comprehensive evaluation. The analytical solutions describing the plastic instability are proposed and validated. A set of single expressions, which are variation-independent of the material type (CP-Ti, Ti64), PBF-methods and heat-post-processing (HPP) conditions, are obtained using the semi-analytical method. It is found that during the plastic deformation, the mean-free-path for the dislocation storage is the intrinsic length L that is represented by the α/α’ phase width. The uniform elongation corresponding to the onset of necking is primarily controlled by the dislocation recovery factor. The increasing of the dislocation density at the onset-state of necking is mainly determined by the initial dislocation contribution to the flow stress. It results in a linear correlation between the true tensile strength and yield strength.

View all citing articles on Scopus

View full text

Influence of tempering temperature and time on the α′-Ti-6Al-4V martensite

Abstract

Scr. Metall. Mater.

Light Alloys, Metallurgy of the Light Alloys

Titanium Technology