A pinboard by
Anoop Maurya

Researcher, IIT Khargpur


Effect of Scan speed on Laser Manufactured Titanium alloy

Ti alloy which is 90% used in aerospace industry .It's strength to weight ratio is very high.It also used in biomedical application(Bone implant).Various component are manufactured by 3D printing(Laser or Electron beam melting).During Processing various parameter apply like scan speed of beam,Powder feed rate,Applied Voltage etc.All parameters affect the mechanical property of component.


High Temperature Dynamic Response of a Ti-6Al-4V Alloy: A Modified Constitutive Model for Gradual Phase Transformation

Abstract: Dynamic deformation behavior of a commercial Ti-6Al-4V alloy is measured between room temperature and beyond the β-transus temperature with high thermal resolution using a rapid-heating Kolsky bar technique. The high thermal resolution allows for a thorough investigation of the dynamic thermal softening behavior of this alloy including effects related to the transformation from the initial hcp α/bcc β dual phase structure to a full β structure for improved modeling of high temperature dynamic manufacturing processes such as high-speed machining. Data are obtained at an average strain rate of 1800 s−1 from room temperature to 1177 °C, with total heating times limited to 3.5 s for all tests. Short heating times prevent thermal distortion of the Kolsky bar loading waves and can allow an investigation of non-equilibrium mechanical behavior, although no such behavior was identified in this study. Between 800 °C and 1000 °C, a progressive change in the thermal softening rate was observed that corresponded well with the equilibrium phase diagram for this alloy. The dynamic thermal softening behavior in the transformation region is incorporated via a new modification of the Johnson–Cook (J–C) viscoplastic constitutive equation. Rate sensitivity is determined at room temperature by combining Kolsky bar data with quasi-static measurements at strain rates from 7.5 × 10−5 s−1 to 0.16 s−1 and the data are fit using multi-parameter optimization to arrive at a full modified J–C model for Ti-6Al-4V to nearly 1200 °C. In its generic form, the modification factor we propose, G(T), is applicable to any material system undergoing gradual phase transformation over a range of temperatures.

Pub.: 23 Oct '17, Pinned: 07 Nov '17

Microstructural impact on flank wear during turning of various Ti-6Al-4V alloys

Abstract: Titanium alloys typically do not contain hard inclusion phases typically observed in other metallic alloys. However, the characteristic scoring marks and more distinctive micro- and/or macro-chippings are ubiquitously observed on the flank faces of cutting tools in machining titanium alloys, which is the direct evidence of abrasive wear (hard phase(s) in the microstructure abrading and damaging the flank surface). Thus, an important question lies with the nature of the hard phases present in the titanium microstructure. In this work, we present a comprehensive study that examines the microstructural impact on flank wear attained by turning various Ti-6Al-4V bars having distinct microstructures with uncoated carbide inserts. In particular, four samples with elongated, mill-annealed, solution treated & annealed and fully-lamellar microstructures were selected for our turning experiments. After turning each sample, the flank surface of each insert was observed with confocal laser scanning microscopy (CLSM) and analyzed to determine the flank wear behavior in relation to each sample' distinct microstructures. To characterize the microstructure, scanning electron microscopy (SEM) together with Orientation imaging microstructure (OIM) was used to identify and distinguish the phases present in each sample and the content and topography of each phase was correlated to the behavior of flank wear. The flank wear is also affected by the interface conditions such as temperature and pressure, which were estimated using finite element analysis (FEA) models. The temperature dependent abrasion models enable us to estimate the flank wear rate for each microstructure, and are compared with the experimentally measured wear data.

Pub.: 01 Aug '17, Pinned: 07 Nov '17

Full length articleOrientation dependent spheroidization response and macro-zone formation during sub β-transus processing of Ti-6Al-4V alloy

Abstract: In the present study, sub β-transus static annealing was carried out on a (α+β)-warm-rolled (700 °C, 90% thickness reduction) Ti-6Al-4V alloy at 900 °C for various durations (15, 30, 45, 60, 75 and 90 min). The key observation was that the spheroidization response of the constituent α-colonies from the starting warm-rolled material differs significantly during subsequent (α+β)-annealing treatment. While some of the α-colonies underwent an early morphological conversion from lamellar to equiaxed, some others stayed stable for prolonged durations. This unique phenomenon has been examined, for the first time, from an orientation perspective by coupling slip activation, boundary formation, and interfacial energy anisotropy of individual α-colonies with their response to static spheroidization. Orientation of the α-colonies in reference to the loading directions dictate the nature of slip activation (single versus multiple slip; basal or prism <a> slip plus pyramidal 〈c+a〉 slip) during prior (α+β)-rolling. During subsequent static (α+β)-annealing, this factor translates into the relative ease of boundary splitting and thermal grooving for them. Formation of longitudinal boundaries, then set the order of spheroidization for diffusion based coarsening processes during long term annealing. Anisotropy in interfacial energy, owing to the loss of coherency during prior deformation (warm-rolling), creates further orientation dependency in the spheroidization sequence. An immediate consequence of this orientation dependent spheroidization response is realized in the formation of the macro-zones for two-phase Titanium alloys after secondary thermomechanical processing. Some remedial processing strategies are highlighted therein.

Pub.: 01 Aug '17, Pinned: 07 Nov '17

Full Length ArticleCompressive properties of Ti-6Al-4V lattice structures fabricated by selective laser melting: Design, orientation and density

Abstract: Lattice structures have been intensively researched for their light-weight properties and unique functions in specific applications such as for impact protection and biomedical-implant. The advancement of additive manufacturing simplifies the fabrication of lattice structures as opposed to conventional manufacturing and this opens doors to create more designs. There are ample research opportunities to explore the mechanical performance of the lattice structures fabricated by this technology specific to each design. This study filled the research gap by investigating the deformation behaviour and compressive properties of Ti-6Al-4V lattice structures fabricated by a powder bed fusion method from the aspects of design, orientation and density. The results were compared between cubic and honeycomb unit designs, between two orientations and across five different densities. Results showed that both cubic and honeycomb lattice deformed in a layer-by-layer manner for the first tested orientation, where vertical struts were parallel to the compression direction. In the second tested orientation, where lattice struts were angled with respect to the direction of compression, the deformation behaviour was observed as a single diagonal shear band. As the density of the structure increased, the deformation pattern shifted towards diagonal crack similar to a solid part. Honeycomb lattice structure had the highest density efficiency for energy absorption in both orientations and for first maximum compressive strength in the second orientation. Change of orientation significantly affected the efficiency in plateau stress for cubic lattice structure, and compressive property values for honeycomb lattice structure. Comparative studies showed that the first maximum compressive strength and energy absorption of the lattice structures in the first orientation were higher than most of the lattice designs from other literature.

Pub.: 01 Aug '17, Pinned: 07 Nov '17