Hot deformation and recrystallization of a metastable beta titanium ingot

Hot deformation behavior and microstructure evolution of a coarse grain metastable beta titanium alloy (Ti-5Al-5Mo-5V-3Cr) was investigated using uniaxial compression testing followed by a subsequent beta annealing treatment. Compression testing was carried out at 720 °C and strain rates between 0.001-10 s-1 on samples with beta annealed condition and aged microstructure containing high volume fraction of relatively large alpha precipitates. The peak load of the aged samples are higher than the non-aged specimens but they show rather similar steady state flow stress. The subsequent beta annealing treatment on the compressed aged samples leads to breaking down the ingot microstructure and formation of a fully recrystallized beta phase with massive grain refinement (order of millimeter to ∼100 μm). However, after annealing such grain refinement is not seen for the non-aged samples except at high strain rates that showed partial and local recrystallization.

Deformation behaviour of a commercial pure titanium alloy during hot compression testing

The flow curve behaviour and microstructure evolution of commercially pure titanium (CP-Ti) through uniaxial hot compression was investigated at 850 °C and a strain rate of 0.1/s. Electron back scattered diffraction (EBSD) was employed to characterize the microstructure and crystallographic texture development for different thermomechanical conditions. The stress-strain curves of CP-Ti alloy under hot compression displayed a typical flow behaviour of metals undergoing dynamic recrystallization (DRX), which resulted in grain refinement. The critical strain for the onset of DRX was 0.13 using the double differentiation analysis technique. It was also revealed that the texture was markably altered during hot deformation. © (2014) Trans Tech Publications, Switzerland.

A preliminary assessment of machinability of titanium alloy Ti 6Al 4V during thin wall machining using trochoidal milling

Titanium alloys are of great demand in the aerospace and biomedical industries. Most the titanium products are either cast or sintered to required shape and finish machined to get the appropriate surface texture to meet the design requirements. Ti-6Al-4V is often referred as work horse among the titanium alloys due to its heavy use in the aerospace industry. This paper is an attempt to investigate and improve the machining performance of Ti-6Al-4V. Thin wall machining is an advance machining technique especially used in machining turbine blades which can be done both in a conventional way and using a special technique known as trochoidal milling. The experimental design consists of conducting trials using combination of cutting parameters such as cutting speed (vc), 90 and 120 m/min; feed/tooth (fz) of 0.25 and 0.35 mm/min; step over (ae) 0.3 and 0.2; at constant depth of cut (ap) 20mm and using coolant. A preliminary assessment of machinability of Ti-6Al-4V during thin wall machining using trochoidal milling is done. A correlation established using cutting force, surface texture and dimensional accuracy.

Machinability assessment of titanium alloy Ti-6Al-4V for biomedical applications

Titanium alloy (Ti-6Al-4V) has a wide range of application in various fields of engineering. Titanium is mainly used to manufacture aerospace components like landing gear, fuselage, wings, engines etc. and biomedical components like hip joint, knee joint, dental implants etc. Titanium has outstanding material properties such as corrosion resistance, fatigue strength, tensile strength and a very good biocompatibility which makes this material very alluring for biomedical applications. Contrary, the machinability of the material is problematic because of the phase transformations and thus, titanium alloy is a challenge for machining operation. This research is a comparative analysis between the implants manufactured by traditional method of casting and machining. The femoral stem of the hip joint replacement is designed and the component is machined using a five-axis CNC machine.The machined component was subjected to surface roughness testing, tensile testing and bulk hardness testing. The values were compared with the values of titanium implants manufactured by casting. © (2014) Trans Tech Publications, Switzerland.

One-hit machining of titanium alloy (Ti-6al-4v) wall component with trochoidal milling

This research will definitely give guidelines to industries associated with titanium slot machining.

Machining of titanium alloy (Ti-6Al-4V)-theory to application

This article correlates laboratory-based understanding in machining of titanium alloys with the industry based outputs and finds possible solutions to improve machining efficiency of titanium alloy Ti-6Al-4V. The machining outputs are explained based on different aspects of chip formation mechanism and practical issues faced by industries during titanium machining. This study also analyzed and linked the methods that effectively improve the machinability of titanium alloys. It is found that the deformation mechanism during machining of titanium alloys is complex and causes basic challenges, such as sawtooth chips, high temperature, high stress on cutting tool, high tool wear and undercut parts. These challenges are correlated and affected by each other. Sawtooth chips cause variation in cutting forces which results in high cyclic stress on cutting tools. On the other hand, low thermal conductivity of titanium alloy causes high temperature. These cause a favorable environment for high tool wear. Thus, improvements in machining titanium alloy depend mainly on overcoming the complexities associated with the inherent properties of this alloy. Vibration analysis kit, high pressure coolant, cryogenic cooling, thermally enhanced machining, hybrid machining and, use of high conductive cutting tool and tool holders improve the machinability of titanium alloy.

Constitutive modelling of high strength titanium alloy Ti-6Al-4 V for sheet forming applications at room temperature

To enable the design and optimisation of forming processes at room temperature the material behaviour of Ti-6Al-4 V needs to be accurately represented in numerical analysis and this requires an advanced material model. In particular, an accurate representation of the shape and size of the yield locus as well as its evolution during forming is important. In this study a rigorous set of experiments on the quasi-static deformation behaviour of a Ti-6Al-4 V alloy sheet sample at room temperature was conducted for various loading conditions and a constitutive material model developed. To quantify the anisotropy and asymmetry properties, tensile and compression tests were carried out for different specimen orientations. To examine the Bauschinger effect and the transient hardening behaviour in - plane tensile - compression and compression - tensile tests were performed. Balanced biaxial and plane strain tension tests were conducted to construct and validate the yield surface of the Ti-6Al-4 V alloy sheet sample at room temperature. A recently proposed anisotropic elastic-plastic constitutive material model, so-called HAH, was employed to describe the behaviour, in particular for load reversals. The HAH yield surface is composed of a stable component, which includes plastic anisotropy and is distorted by a fluctuating component. The key of the formulation is the use of a suitable yield function that reproduces the experimental observations well for the stable component. Meanwhile, the rapid evolution of the material structure must be captured at the macro - scale level by the fluctuating component embedded in the HAH model. Compared to conventional hardening equations, the proposed model leads to higher accuracy in predicting the Bauschinger effect and the transient hardening behaviour for the Ti-6Al-4 V sheet sample tested at room temperature.

Materials machining study of titanium alloy using a high speed camera

The research aim is to study and analyze the shear zone by application of merchant circle during machining of titanium alloy (Ti6Al4V). The thermo-mechanical reaction during machining plays an important role in defining machinability of titanium alloys. The scientific community is concerned about machining of titanium alloy due to problems occurring in the shear zone that affect tool life. Studying the cutting action contributes to understanding and addressing these problems effectively. For this purpose, an experimental setup, utilizing a high speed camera will be used to study the shear zone. The shear zone characteristics are studied by analyzing the images captured by a high speed camera placed near to the shear zone during machining. The experimental design consists of conducting a series of turning trials using combination of cutting parameters namely constant spindle speed (n) 770 rpm; feed rate (f) of 2 and 4 mm/rev; and depth of cut (d) of 1 and 2 mm. The length of cut (L) of 10 mm remains constant and no coolant is used for all trials. The images obtained from the camera are analyzed against the theory of orthogonal cutting using merchants circle.

Design of a new biocompatible ti-based shape memory alloy and its superelastic deformation behaviour

Titanium-nickel (Ti-Ni) shape memory alloys have been widely used for biomedical applications in recent years. However, it is reported that Ni is allergic and possibly carcinogenic for the human body. Therefore, it is desirable to develop new Ni-free Ti-based shape memory alloys for biomedical applications. In the present study, a new Ti-18Nb-5Mo-5Sn (wt.%) alloy, containing only biocompatible alloying elements, was designed with the aid of molecular orbital method and produced by vacuum arc melting. Both β and α″ martensitic phases were found to coexist in the alloy after ice-water quenching, indicating the martensitic transformation. The phase transformation temperatures of the Ti-18Nb-5Mo-5Sn alloy were M_s = 7.3 °C, M_f = −31.0 °C, A_s = 9.9 °C, and A_f = 54.8 °C. Superelasticity was observed in the alloy at a temperature higher than the A_f temperature. A totally recovered strain of 3.5 % was achieved for the newly designed Ti-based shape memory alloy with a pre-strain of 4 %.

Study on the role of stearic acid and ethylene-bis-stearamide on the mechanical alloying of a biomedical titanium based alloy

The present study examines the influence of different contents and types of process control agent (PCA), i.e., stearic acid (SA) and ethylene-bis-stearamide (EBS), on the microstructural evolution and characteristics of Ti-16Sn-4Nb (wt pct) alloy powders and bulk samples. The characterization of the powders and bulk samples was carried out by using chemical analysis, optical microscopy, scanning electron microscopy (SEM) combined with energy-dispersive spectrometry (EDS), and X-ray diffractometry. Results indicated that the powder recovered from the ball milling containers increased with increasing amounts of SA and EBS. Furthermore, adding more SA or EBS to the powder mixture resulted in a considerably smaller particle size, with a flaky-shaped morphology for the given ball milling time. Also, a slightly higher effectiveness was found for EBS when compared to SA. Meanwhile, the addition of both SA and EBS led to a delay in the alloy formation during mechanical alloying (MA) and caused contamination of the material with mainly carbon (C) and oxygen (O). An optimum amount of 1 wt pct PCA led to a good balance between cold welding and fracturing, and thus favored the formation of the titanium alloy. The microstructural observation of the bulk alloy showed a homogeneous distribution of fine Nb-rich ß-phase colonies within the α-Ti matrix with the addition of PCA less than 1 wt pct.