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•The self-assembled growth mechanisms of Ni–Ti–O nanotubes and nanopores on NiTi alloys are discussed.•The factors that influence the structural growth and characteristics are ...summarized.•The influence of the structures on the corrosion behavior, Ni ion release, and biological performances is reviewed.•Future research efforts of self-assembled anodization of NiTi alloys are suggested.
Nearly equiatomic nickel-titanium (NiTi) alloys are used in many biomedical applications due to their favorable properties, but in some cases, the surface properties such as corrosion resistance and biological characteristics may be inadequate, especially for clinical applications. Electrochemical self-assembly is an emerging surface modification method for valve metals and their alloys and the ordered oxide nanostructures produced by this method not only increase the corrosion resistance, but also regulate the cell behavior. Herein, recent advances pertaining to self-assembled anodization of NiTi alloys and biomedical applications are described. In particular, the influence of the preparation parameters on the morphology, microstructure, composition, corrosion behavior, Ni ion release, and biological response of self-assembled Ni–Ti–O nanotubes and nanopores are comprehensively analyzed and discussed.
Nucleation of in‐service cracks leads to detrimental consequences for structural components of near‐α titanium alloys subjected to fatigue loads. Experimental observations show that the fatigue ...initiation facets usually form in certain crystallographic orientation ranges of “hard” primary α grains which differ between pure and dwell fatigue loads. In this manuscript, a comparative study has been performed using several fatigue indicator parameters (FIPs) to assess their ability to predict the location of fatigue crack nucleation in near‐α titanium alloy microstructures. All selected FIPs are implemented within the same polycrystalline plasticity finite element modeling framework to facilitate one‐to‐one comparisons. Comparison on predictability of critical initiation locations and their crystallographic orientations is studied for incorporated FIPs under pure and dwell fatigue. The critical locations predicted by some FIPs were found to be close to each other, and consistent with the crystallographic orientation ranges from fractography measurements, in addition to the range transition from pure to dwell fatigue loads. Critical locations from slip driven FIPs are obtained to be several grains away from that of the former ones and are inclined to capture orientations of slip traces from experiments.
Highlights
Comparative study of is performed on different fatigue indicator parameters in the same CPFE framework.
Some FIPs show similar critical sites and crystallography thereof, consistent with experimental data.
CP results of these FIPs capture the experimental orientation range transition of critical sites from pure to dwell fatigue load.
Proposed FIP, solely based on dislocation density, is validated through comparison with other FIPs and experiments.
Abstract
Individually, increasing the concentration of either oxygen or aluminum has a deleterious effect on the ductility of titanium alloys. For example, extremely small amounts of interstitial ...oxygen can severely deteriorate the tensile ductility of titanium, particularly at cryogenic temperatures. Likewise, substitutional aluminum will decrease the ductility of titanium at low-oxygen concentrations. Here, we demonstrate that, counter-intuitively, significant additions of both Al and O substantially improves both strength and ductility, with a 6-fold increase in ductility for a Ti-6Al-0.3 O alloy as compared to a Ti-0.3 O alloy. The Al and O solutes act together to increase and sustain a high strain-hardening rate by modifying the planar slip that predominates into a delocalized, three-dimensional dislocation pattern. The mechanism can be attributed to decreasing stacking fault energy by Al, modification of the “shuffle” mechanism of oxygen-dislocation interaction by the repulsive Al-O interaction in Ti, and micro-segregation of Al and O by the same cause.
Titanium alloys are widely used in the manufacture of aircraft and aeroengine components. However, tool wear is a serious concern in milling titanium alloys, which are known as hard-to-cut materials. ...Trochoidal milling is a promising technology for the high-efficiency machining of hard-to-cut materials. Aiming to realize green machining titanium alloy, this paper investigates the effects of undeformed chip thickness on tool wear and chip morphology in the dry trochoidal milling of titanium alloy Ti-6Al-4V. A tool wear model related to the radial depth of cut based on the volume of material removed (VMR) is established for trochoidal milling, and optimized cutting parameters in terms of cutting speed and axial depth of cut are selected to improve machining efficiency through reduced tool wear. The investigation enables the environmentally clean rough machining of Ti-6Al-4V.
Titanium and its alloys are employed as medical materials because of their low Young's modulus, excellent biocompatibility, and superior corrosion resistance. This work aimed to characterize the ...electrochemical behavior of titanium Ti-CP2 and alloys Ti-6Al-2Sn-4Zr-2Mo, and Ti-6Al-4V. Ti and Ti-alloys were exposed to Ringer´s solution at room temperature. The electrochemical characterization was made by cyclic potentiodynamic polarization (CPP) and electrochemical noise technique (EN). Two different methods filtered EN signal, the polynomial method and the potential spectral density (PSD). Also, the Wavelets method, where energy dispersion plots were obtained. Results indicated that Ti-6Al-2Sn-4Zr-2Mo presented less dissolution when exposed in Ringer analysis by ψ0. The wavelet method showed a diffusion process occurring on the surface.
A β titanium alloy was fabricated horizontally and vertically at two different energy densities by selective laser melting. The microstructures of the as-fabricated samples were examined using a ...range of characterization techniques and the properties evaluated by tensile testing. It was found that the samples that were horizontally built at the lower energy density were dominated by both β and athermal ω phases while the vertically built samples consist of not only β and ω but also nano-sized α laths. Increased energy density led to a significant increase of α in horizontally built samples which tended to constitute a grid-like structure in the β matrix. All the α-bearing samples showed preferential α variant selection and pronounced α micro-texture. The α-free samples all showed high 0.2% yield strengths (922-934 MPa), high ultimate tensile strengths (935-939 MPa) and good ductility (10.2%–13.8% elongation) whereas the α-bearing samples all exhibited poor ductility (elongation < 1.2%). A significant anisotropy in plasticity was observed in the samples made with the lower energy density. Transmission electron microscopy examination revealed that the α-free samples experienced global plastic deformation via both long-range dislocation slipping and twinning whereas the α-bearing samples underwent localised plastic deformation where slipping was either interrupted by the nano-sized α laths or contained within the α-grid demarcated β matrix, which may account for their poor ductility.
Cryogenic machining has emerged as a sustainable technique that reflects in terms of reduced environmental effects, superior part quality, and lesser resource consumption. However, further ...exploration of machinability and sustainability improvements using this technique will help the manufacturing industry to adopt it as an alternative to conventional techniques. In this government-supported work, the machinability of Ti–6Al–4V is assessed at five different cutting speeds (70, 80, 90, 100, and 110 m/min) under wet and cryogenic environments. This article presents a detailed analysis of tool wear (flank and crater wear), power consumption, and surface roughness to seek improvements in machinability of Ti–6Al–4V using cryogenic turning in comparison to wet turning. To investigate the sustainability aspects of cryogenic and wet turning, results are also analyzed in terms of total machining cost and carbon emissions that remain relatively less explored in literature. The results show higher crater wear under a wet environment relative to the cryogenic environment at most of the cutting speeds. However, tool life is improved (by up to 125%) using cryogenic turning in comparison to wet turning exclusively at higher cutting speeds (100 and 110 m/min). Reduced power consumption (by up to 23.4%) and surface roughness (by up to 22.1%) are obtained using cryogenic turning than wet turning at all cutting speeds. It is noted that machining cost is reduced (by up to 27%) using cryogenic turning in comparison to wet turning, especially at higher cutting speeds. Cryogenic turning is proved to be better in terms of environmental aspects as it enables a reduction in overall carbon emissions (by up to 22%) at higher cutting speeds.
To control the surface metamorphic layer and improve the performance of the workpiece, a combination of measurement and simulation is employed to obtain the force and temperature fields in TC17 ...milling. Based on the thermo-mechanical coupling, the formation mechanism of the surface metamorphic layer is analyzed. In addition, the influence of parameters on the surface characteristics is also studied. The results show that the milling force varies from 58.39 to 170.7 N, the temperature effect layer increases from 102 μm to 210 μm, and the effective strain layer increases from 38 μm to 145 μm within the experiment parameters. The thermal-mechanical coupling has a significant effect on residual stress. The surface compressive residual stress varies from − 206 to − 314 MPa, and the residual stress layer depth fluctuates by 30 μm. With the enhancement of thermal-mechanical coupling, the microhardness fluctuation does not exceed 20HV
0.025
, and the maximum microhardness can reach 384HV
0.025
. Moreover, the microhardness effected layer remains at 40 μm regardless of parameters enhanced, revealing that microhardness is insensitive to the process parameters. The plastic deformation layer depth alternates between 17 and 28 μm, indicating that it is little affected by thermal-mechanical coupling. Finally, the established model can accurately predict surface roughness and residual stress.
Additive Layer Manufacturing (ALM) is becoming a more widely accepted method for the production of near net-shape products across a range of industries and alloys. Depending on the end application, a ...level of process substantiation is required for new parts or alloys. Prior knowledge of the likely process parameter ranges that will provide a target region for the process integrity can save valuable time and resource during initial ALM trials. In this paper, the parameters used during the powder bed ALM process have been taken from the literature and the present study to construct normalised process maps for the ALM process by building on an approach taken by Ion et al. in the early 1990's (J.C. Ion, H.R. Shercliff, M.F. Ashby, Acta Metallurgica et Materialia 40 (1992) 1539–1551). These process maps present isopleths of normalised equivalent energy density (E0*) and are designed to provide a practical framework for comparing a range of ALM platforms, alloys and process parameters and provide a priori information on microstructure. The diagrams provide a useful reference and methodology to aid in the selection of appropriate processing parameters during the early development stages. This paper also applies the methodology to worked examples of Ti–6Al–4V depositions processed using different Electron Beam Melting parameters.
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•A new framework is presented for data-driven fatigue life prediction of AM alloys.•Computational strategy is demonstrated for the CDM based machine learning method.•Predicted fatigue lives of AM ...titanium alloys are verified by experimental data.•Parametric studies are investigated on prediction performance and fatigue lives.
Additive manufacturing (AM) technology has been widely employed in the fabrication of titanium alloy parts for aerospace engineering applications. In this paper, a damage mechanics based machine learning framework is presented for the data-driven fatigue life prediction of AM titanium alloy. At first, a theoretical framework including the damage mechanics based fatigue models and random forest model is presented for the fatigue damage analysis and life prediction of the AM titanium alloys under cyclic loadings. Second, a computational methodology is demonstrated in detail from two aspects, that is, the numerical implementation of the damage mechanics based fatigue models and the construction process of the random forest model. After that, fatigue life predictions are carried out for the AM titanium alloy smooth and notched specimens under different stress levels and stress ratios. The predicted results are compared with the experimental data to verify the proposed method. Finally, parametric studies are investigated on the prediction performance and fatigue lives for the AM titanium alloys.
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