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Technical Paper

Ti/TiN Multilayer Coatings on Titanium Alloys

Titanium alloys have been widely used in manufacturing of fans, compressor disks, and blades of advanced aircraft engines. However, titanium alloys are very sensitive to fretting fatigue damage, which may affect the safe reliability of the aircraft engine compressor. The multilayer coatings seem to be the most promising coating concept due to many requirements (e.g. multifunctional character, moderate residual stresses, good adherence to metallic substrates, proper hardness to toughness ratio and low friction coefficients) for titanium alloys exposed to complex wear conditions. This work aims the development of techniques for production of Ti/TiN multilayer coatings by Electron Beam Physical Vapor Deposition (EB-PVD) in order to define the influence of the number and thickness of the layers in the surface hardness of Ti-13Nb-13Zr alloy produced by powder metallurgy (P/M) from elemental hydrides.
Technical Paper

Study of Milling and Sintering of Titanium Hydride Powders Aiming the Reduction of Oxygen as Interstitial Element

Contamination of titanium by oxygen is inevitable during its processing by powder metallurgy (PM). When dissolved interstitially in the crystal lattice of titanium, oxygen exerts a great influence on strength and other mechanical properties. In this paper we investigated the effects of milling and sintering of titanium hydride powders on the levels of oxygen in sintered samples. To minimize contamination, milling was carried out under argon atmosphere and the manipulation of powders was performed inside a glove box. Samples were milled at two different particles sizes, isostatically pressed and sintered at 1000°C and 1200°C. The results indicated that the oxygen content in the final samples is mainly influenced by the level of oxygen in the starting powders and the particle size of these powders.
Technical Paper

Porosity Control in Ti-13Nb-13Zr Alloy Produced by Powder Metallurgy

Titanium and titanium alloys are excellent candidates for aerospace and surgical implants applications owing to their high strength to weight ratio and good corrosion resistance. Among the titanium alloys recently developed, Ti-13Nb-13Zr is distinguished for presenting low modulus of elasticity, high mechanical resistance and superior biocompatibility, suitable for springs, bellows, surgical implants and aerospace parts with high resistance to shock and explosion damage. The alloys processing by powder metallurgy eases the obtainment of parts with complex geometry and near-net shape. In this work, results of the porosity control in the Ti-13Nb-13Zr alloy produced by powder metallurgy are presented. The samples were characterized for phase composition, microstructure and microhardness by X-ray diffraction, scanning electron microscopy and Vickers indentation, respectively. It was shown that the porosity level depends on the compaction pressures, sintering temperatures and holding times.
Technical Paper

Microstructural investigation of Ti-48Al-2Cr-2Nb (at.%) obtained by powder metallurgy using hot uniaxial pressing

The aim of this paper is to analyze the microstructural development in samples of Ti-48Al-2Cr-2Nb (at.%) alloys obtained by powder metallurgy (P/M). This alloy has potential applications when high operating temperatures are required, e. g. turbines, aerospace applications, automotive engines valves and turbocharger rotors. The elementary powders were mixed for 1 hour, cold uniaxially pressed at 60 MPa and sintered at 1100°C, for 1 hour, under vacuum. Then, the specimens were milled and submitted to a second stage that included cold isostatic pressing (400 MPa) with subsequent hot uniaxial pressing (20 MPa), between 900 up to 1200°C, for 2 hours, in argon atmosphere. The alloys were characterized by XRD (X-ray diffraction), SEM (Scanning Electron Microscopy), EDS (Energy Dispersive Spectroscopy) and Vickers microhardness measurements. The results indicated the viability of the route and the tendency of a lamellar microstructure in high sintering temperatures.
Technical Paper

Development of Titanium Nitride Coatings in Titanium Alloys by Electron Beam Physical Vapor Deposition

It is observed an increasing interest in using titanium nitride (TiN) coatings to improve the wear properties of Ti alloys. An important method is the Electron Beam Physical Vapor Deposition (EBPVD) that is a form of deposition in which a target anode is bombarded with an electron beam given off by a charged tungsten filament under high vacuum, producing a thin film in a substrate. In this work are presented results of the target and substrate production using Ti (C.P.), Ti-6Al-4V and Ti-13Nb-13Zr by powder metallurgy. Samples were produced by mixing of initial metallic powders followed by uniaxial and cold isostatic pressing with subsequent densification by sintering between 900 to 1500 °C, in vacuum. Sintered samples were characterized for phase composition, microstructure and microhardness by X-ray diffraction, scanning electron microscopy and Vickers indentation, respectively. It was shown that the samples were sintered to high densities and presented homogeneous microstructure.
Technical Paper

Development of Techniques for Gamma Ti-Al Production

Gamma Ti-Al (γ Ti-Al) has excellent mechanical properties and oxidation/corrosion resistance at elevated temperatures (above 700°C), which makes it a possible replacement for traditional Ni based superalloy components in aircraft turbine engines and in orbital platform vehicles. The alloy design and efficient routes of TiAl processing are important technological challenges. In this work, samples of Ti-48Al-2Cr-2Nb (at.%) were produced by powder metallurgy processes. Using powder metallurgy, samples were prepared from elemental and pre-alloyed powders mixed for 2 h, followed by cold uniaxial and isostatic pressing and sintered between 1100°C up to 1400°C, for 1 h, under vacuum. After metallographic preparation, samples were characterized by SEM (Scanning Electron Microscopy), X-ray diffraction (XRD), density analyses and Vickers microhardness measurements.