Creep behavior and surface characterization of a laser surface nitrided Ti-6Al-4V alloy

Laser surface nitriding of a Ti-6Al-4V alloy is studied with the aim of increasing creep resistance. A detailed characterization of the surface and cross section of the nitrided laser surface was carried out by optical/scanning electron microscopy and X-ray diffraction techniques. the microstructure of the surface-nitrided Ti-6Al-4V consists of TiN dendrites distributed in a martensitic titanium matrix. Finally, the mechanical properties in terms of microindentation hardness and creep resistance were evaluated. Constant load creep tests were conducted on a standard creep machine at different stress levels at 500 degrees C, 600 degrees C and 700 degrees C. Results indicated that the creep rates of the laser nitrided alloy were lower than those of the untreated material and the microhardness of the surface was improved to 1100 VHN compared with the 340 VHN of the substrate. (C) 2013 Elsevier B.V. All rights reserved.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Inst Tecnol Aeronaut ITA DCTA, BR-12228900 Sao Jose Dos Campos, SP, BrazilUniversidade Federal de São Paulo UNIFESP, BR-12231280 Sao Jose Dos Campos, SP, BrazilEscola Engn Lorena EEL DEMAR USP, BR-12600970 Lorena, SP, BrazilUniv Politecn Madrid, E-28040 Madrid, SpainUniversidade Federal de São Paulo UNIFESP, BR-12231280 Sao Jose Dos Campos, SP, BrazilWeb of Scienc

Performance of 3Y-TZP bioceramics under cyclic fatigue loading

In this work, the static mechanical properties and cyclic fatigue life of 3 mol. (%) Y2O3-stabilized tetragonal zirconia polycrystalline (3Y-TZP) ceramics were investigated. Pre-sintered samples were sintered in air at 1600 °C for 120 minutes, and characterized by X ray diffraction and scanning electronic microscopy. Hardness and fracture toughness were determined by Vicker's indentation method, and Modulus of Rupture was determined by four-point bending testing. Fully dense sintered samples, near to 100% of theoretical density, presented hardness, fracture toughness and bending strength of 13.5 GPa, 8.2 MPa.m½ and 880 MPa, respectively. The cyclic fatigue tests were also realized using four-point bending testing, within a frequency of 25 Hz and stress ratio R of 0.1. The increasing of load stress lead to decreasing of the number of cycles and the run-out specimens number. The tetragonal-monoclinic (t-m) ZrO2-transformation observed by X ray diffraction contributes to the increasing of the fatigue life. The 3Y-TZP samples clearly presents a range of loading conditions where cyclic fatigue can be detected

Fatigue behavior of 3%Y2O3-doped ZrO2 ceramics

The objective of this work was to evaluate the cyclic fatigue strength of a commercial pre-sintered tetragonal zirconia ceramics for dental systems, and to determine the main mechanical properties. Samples were sintered in air at 1600 °C for 120 min with heating and cooling rate of 10 °C/min. The sintered specimens were characterized by X-ray diffraction and scanning electron microscopy. Hardness and fracture toughness were determined using the Vicker's indentation method. The strength was determined by four-point bending tests. The cyclic fatigue tests were realized as four-point bending tests within a frequency of 25 Hz and a stress ratio R of 0.1. The Weibull analysis was employed in order to perform failure probability calculations. Sintered specimens presented average values of hardness, fracture toughness and bending strength near to 13.5 GPa, 8 MPa m1/2 and 900 MPa, respectively. The fatigue tests results allow concluding that the fatigue strength limit over 5 × 106 stress cycles is about 550 MPa or around 63% of the static strength of this material. The tetragonal–monoclinic (t–m) zirconia transformation observed by X-ray diffraction of fractured surfaces occurs during cyclic loading and the fracture of specimens. The 3Y-TZP samples clearly present a range of loading conditions where cyclic fatigue can be detected. The fatigue strength limit around 550 MPa is appropriate for application in dental implant parts

Short-term creep properties of Ti-6Al-4V alloy subjected to surface plasma carburizing process

The aim of this study was to investigate the short-time creep behavior of Ti-6Al-4V by plasma carburizing, which was performed at 725 °C for 6 h in a 50% Ar – 45% H2 – 5% CH4 gas mixture. Nano and microhardness testing, optical microscopy, TEM, X-ray diffraction and optical profilometry were used to characterize the samples. Furthermore, short-term creep tests were performed under a constant tensile load in air at 600 °C using a dead-weight-creep-rupture machine. The carburizing treatment resulted in a compound layer measuring approximately 1.7 μm in thickness with a hardness of 815 HV and a composition of TiC0.66. The creep properties of the “Widmanstätten + carburized” specimens were improved relative to those of untreated specimens. TEM and fracture analysis indicated creep deformation process attributed mainly to α phase deformation and fracture by intergranular decohesion