Effects of double aging heat treatment on the microstructure, Vickers hardness and elastic modulus of Ti-Nb alloys

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)Aging heat treatment can be a good way to optimize mechanical properties, changing the microstructure, and hence, the mechanical behavior of Ti alloys. The effects of aging heat treatments on beta-type Ti-30Nb alloy were investigated to evaluate the kinetics of alpha '' -> alpha + beta transformation. The results obtained from differential scanning calorimetry and high-temperature X-ray diffraction experiments indicated the complete decomposition of orthorhombic alpha '' phase at close to 300 degrees C, followed by a phase precipitation at 470 degrees C. The aging heat treatments also enabled us to observe a transformation sequence alpha '' -> beta + omega -> beta + omega + alpha, indicating martensite decomposition and omega phase precipitation at 260 degrees C after 2 h, followed by a phase nucleation after heating at 400 degrees C for 1 h. The elastic modulus and Vickers hardness of Ti-30Nb alloy were found to be very sensitive to the microstructural changes caused by heat treatment. (C) 2011 Elsevier Inc. All rights reserved.627673680Fundação 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)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

Correlations between aging heat treatment, omega phase precipitation and mechanical properties of a cast Ti-Nb alloy

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Ti-Nb alloys were arc melted in a water-cooled copper hearth in an inert atmosphere. After preparation, the samples were centrifugally cast in copper molds, and rapidly cooled, resulting in a martensitic microstructure. They were then aged at different temperatures. The microstructural characterization of this material suggested that martensite decomposition occurred, leading to precipitation of alpha, beta and omega phases. Aging at higher temperatures led to to phase decay. Mechanical characterization indicated that the heat treatment enhanced the strength and ductility of the alloys. Correlations between heat treatment, omega precipitation and mechanical behavior are discussed. (C) 2010 Elsevier Ltd. All rights reserved.32423872390Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Hexagonal martensite decomposition and phase precipitation in Ti-Cu alloys

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)The mechanical behavior of Ti-Cu alloys can be improved by controlling Ti(2)Cu precipitation. In eutectoid alloys, such precipitation can be achieved by the decomposition of martensite in response to aging heat treatment. The purpose of this work is to discuss the evolution of precipitates during the decomposition of hexagonal martensite in Ti-Cu alloys. First, samples with near-eutectoid compositions were prepared in an arc furnace equipped with a non-consumable tungsten electrode and water-cooled copper hearth under a high purity argon atmosphere. After chemical homogenization at a temperature in the beta field, the samples were water-quenched and examined by differential scanning calorimetry and high-temperature X-ray diffraction. The results indicate that rapidly quenched near-eutectoid Ti-Cu alloys present Ti(2)Cu precipitates. Regardless of the cooling rate applied, such precipitation is unavoidable. No evidence of beta phase stabilization was found in the rapidly quenched samples. Precipitation temperatures of coherent and incoherent phases of 415 degrees C and 550 degrees C, respectively, were determined from the differential scanning calorimetry measurements. Ti(2)Cu precipitation was examined in situ by high temperature X-ray diffraction experiments. The total decay of martensite was found to occur above 575 degrees C. Vickers hardness testing of aged samples revealed a correlation between phase precipitation and hardening. (C) 2011 Elsevier Ltd. All rights reserved.324189046084613Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Microstructure of directionally solidified Ti-Fe eutectic alloy with low interstitial and high mechanical strength

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)The performance of Ti alloys can be considerably enhanced by combining Ti and other elements, causing an eutectic transformation and thereby producing composites in situ from the liquid phase. This paper reports on the processing and characterization of a directionally solidified Ti-Fe eutectic alloy. Directional solidification at different growth rates was carried out in a setup that employs a watercooled copper crucible combined with a voltaic electric arc moving through the sample. The results obtained show that a regular fiber-like eutectic structure was produced and the interphase spacing was found to be a function of the growth rate. Mechanical properties were measured using compression, microindentation and nanoindentation tests to determine the Vickers hardness, compressive strength and elastic modulus. Directionally solidified eutectic samples presented high values of compressive strength in the range of 1844-3000 MPa and ductility between 21.6 and 25.2%. (C) 2011 Elsevier B.V. All rights reserved.33314047Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq