Preparation, processing and characterization of titanium alloys with high mechanical strength based alloy Ti-5553

Orientador: Rubens Caram JúniorDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecânicaResumo: Em segmentos industriais bastante distintos como o aeroespacial e o médico, o uso de titânio e suas ligas na fabricação de dispositivos tem aumentado de forma consistente nos últimos anos. O emprego desse metal de forma tão diversificada, seja em motores a jatos ou em implantes ortopédicos, se deve a suas características únicas, ou seja, elevada resistência mecânica, baixa densidade, alta resistência à corrosão e ótima biocompatibilidade. Estudos realizados nos últimos anos e associados ao uso estrutural do titânio nos setores aeroespacial e médico/odontológico têm focado o desenvolvimento de ligas de titânio tipo ? metaestáveis. O presente estudo tem como objetivo discutir a preparação, processamento e caracterização da liga metaestável Ti-5553 (Ti-5Al-5V-5Mo-3Cr-0,5Fe) e de outras duas ligas com composições modificadas pela adição de nióbio em substituição ao vanádio. Tais ligas foram preparadas por meio de fusão em forno a arco, deformadas plasticamente a quente por forjamento a quente e submetidas a dois diferentes tratamentos térmicos de envelhecimento: BASCA (Beta-annealed Slow Cooled and Age) e STA (Solution Treatment and Age). Na etapa de caracterização foram utilizadas as técnicas de microscopia óptica e eletrônica de varredura, medidas de módulo de elasticidade, medidas de dureza Vickers e ensaios de tração. Os resultados indicam que a substituição do vanádio pelo nióbio não modificou as principais características da liga Ti-5553, particularmente, sua elevada resistência mecânica e baixa cinética de transformações de fases. O tratamento térmico BASCA resultou em maior ductilidade, enquanto que o tratamento STA resultou em maior limite de resistência. À medida que o V foi substituído pelo Nb, amostras submetidas ao tratamento térmico BASCA tiveram suas respectivas resistências mecânicas aumentadas, passando de 1.147 MPa para 1.227 MPa. À medida que o teor de Nb aumentou, a ductilidade reduziu-se de 10,3 % para 6,8 %. Por outro lado, amostras submetidas ao tratamento STA apresentaram redução de resistência mecânica com o aumento do teor de Nb, enquanto que a ductilidade foi levemente reduzida. Em geral, a substituição do V pelo Nb não resultou em alterações significativas no comportamento mecânico da liga Ti-5553Abstract: In well different industrial segments such as aerospace and medical, the use of titanium and its alloys in the manufacturing of devices has increased consistently in recent years. The use of such metal in so diverse manner, either in jet engines or orthopedic implants, is due to its unique characteristics, specifically high mechanical strength, low density, high corrosion resistance and good biocompatibility. Recent studies associated with the structural use of titanium in the aerospace and medical/dental sectors have focused on the development of ? metastable titanium alloys. This study aims to discuss the preparation, processing and characterization of the ? metastable Ti-5553 alloy (Ti-5Al-5V-5Mo-3Cr-0.5Fe) and two alloys with compositions modified by the addition of niobium to replace vanadium. Such alloys were prepared by arc melting, deformed plastically by hot forging and submitted to two different aging heat treatments: BASCA (Beta-annealed Slow Cooled and Age) and STA (Solution Treatment and Age). Characterization was carried out by applying optical microscopy and scanning electron microscopy, measurements of elastic modulus, Vickers hardness and tensile tests. The results suggest that the replacement of vanadium by niobium does not modify the main characteristics of the Ti-5553, particularly, its high mechanical strength and the low kinetic of phase transformations. Application of the BASCA heat treatment resulted in higher ductility, while the STA treatment resulted in higher tensile strength. As V was replaced by Nb, samples subjected to BASCA heat treatment had their mechanical strengths increased, from 1147 MPa to 1227 MPa. As the Nb content increased, ductility dropped from 10.3% to 6.8%. On the other hand, samples subjected to STA presented a decrease in mechanical strength with increasing Nb content, while ductility was slightly reduced. In general, the replacement of V by Nb has not resulted in significant changes in the Ti-5553 alloy mechanical behaviorMestradoMateriais e Processos de FabricaçãoMestre em Engenharia Mecânic

Isothermal omega assisted alpha phase precipitation and microstructural evolution of an aged Ti-30Nb-3Fe alloy

The mechanical behavior of metastable β Ti alloys can be controlled through heat treatments. Thus, the relationship between the precipitation of α phase and the mechanical properties of these alloys is of special interest. In this work, the microstructure evolution of Ti-30Nb-3Fe alloy during aging heat treatments was evaluated using optical microscopy, scanning electron microscopy and X-ray diffraction. Moreover, Vickers hardness and elastic modulus were measured as a function of aging time. Finally, the ultimate strength and ductility of the alloy aged at 500 °C was assessed by tensile tests. In comparison to a Ti-30Nb alloy, the addition of Fe lowered the β-transus temperature, decreased the martensite start temperature to a value below room temperature, increased the precipitation temperature and reduced the dissolution temperature of ω phase, and lastly, decreased the α phase precipitation temperature. Low heating rates enabled isothermal ω phase precipitation and growth, providing favorable conditions for α phase precipitation and increasing the amount of α phase precipitates. Compared to the solution heat-treated and water-quenched condition, aging heat-treated Ti-30Nb-3Fe alloy presented higher Vickers hardness and mechanical strength, without significant loss of ductility233CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP405054/2016-588887.357955/2019-002016/24693-3The authors gratefully acknowledge the LNNano (National Nanotechnology Laboratory) at the CNPEM (National Center for Research on Energy and Materials) for allowing access to its SEM facilities. We also acknowledge the financial support of the Brazilian research funding agencies FAPESP (State of São Paulo Research Foundation) for Grant #2016/24693-3, CNPq (National Council for Scientific and Technological Development) for Grant #405054/2016-5, and CAPES/PNPD (Coordination for the Improvement of Higher Education Personnel) for Grant #88887.357955/2019-00. We thank the Brazilian Niobium Mining and Processing Company CBMM for supplying the Nb used in this stud

Heat treatment, alpha phase precipitation and mechanical properties of Ti-5553 alloy modified by the addition of Nb

Orientador: Rubens Caram JúniorTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecânicaResumo: O uso industrial do titânio e suas ligas aumentou consideravelmente nos últimos anos, principalmente no setor aeroespacial. Aplicações desse metal em diversos segmentos, desde componentes estruturais em aeronaves até implantes ortopédicos e dentários, estão associadas às suas propriedades únicas, tais como elevada relação entre resistência mecânica e densidade, alta resistência à corrosão e ótima biocompatibilidade. Recentemente, o desenvolvimento de novas ligas de titânio do tipo ? metaestáveis tem recebido bastante atenção, pois essa classe de liga de titânio pode apresentar altíssima resistência mecânica - um dos principais interesses da indústria aeroespacial-, bem como porque pode ser obtida a partir de elementos metálicos biocompatíveis, possibilitando sua aplicação como biomaterial. O presente estudo tem como meta investigar a precipitação da fase ? assistida pela fase ? na liga comercial Ti-5553 (Ti-5Al-5V-5Mo-3Cr) e em uma versão dessa liga modificada pela substituição do elemento vanádio por nióbio. As amostras foram preparadas por meio de fusão em forno a arco, deformadas plasticamente por forjamento rotativo a quente e submetidas a diferentes rotas de tratamentos térmicos de envelhecimento, constituídas por patamares de pré-envelhecimento e variações das taxas de aquecimento até a temperatura de envelhecimento. Na etapa de caracterização foram utilizadas as técnicas de microscopia óptica, eletrônica de varredura e eletrônica de transmissão, medidas de dureza Vickers, ensaios de tração e ensaios de compressão. Os resultados indicam que a substituição do vanádio pelo nióbio não modificou as principais características da liga Ti-5553, particularmente sua elevada resistência mecânica e baixa cinética de transformações de fases. Concluiu-se que tratamentos térmicos realizados sob reduzidas taxas de aquecimento favorecem a precipitação fina da fase ?, enquanto que taxas de aquecimento mais elevadas resultaram em crescimento de agulhas de fase ?, influenciando, assim, o comportamento mecânico das amostras. Observou-se também que a aplicação tratamentos térmicos de pré-envelhecimento resultou em maiores níveis de resistência mecânica em relação a tratamentos de envelhecimento direto. A substituição do V por Nb promoveu leve aumento na ductilidade. Porém, a aplicação de diferentes tratamentos térmicos não alterou os mecanismos de fratura, classificados como quase clivagem, ou clivagem com dimplesAbstract: The industrial use of titanium and its alloys has increased considerably in the last years, particularly in the aerospace sector. Applications of this metal in different segments, since aircraft structural components to orthopedic and dental implants, are associated to its unique properties, such as high strength-to-density ratio, high corrosion resistance and excellent biocompatibility. Recently, the development of new ? metastable titanium alloys has received much attention, especially because this titanium alloy class may present high mechanical strength - what can be appointed as one of the main aerospace industry's interest, as well because it can be obtained from biocompatible metal elements, making possible its application as biomaterial. The present study aims to investigate the precipitation of ? phase assisted by ? phase in the commercial alloy Ti-5553 (Ti-5Al-5V-5Mo-3Cr) and in a version of this alloy which was modified by replacing the vanadium with niobium element. The samples were prepared by arc melting, hot worked by swaging and subjected to different aging heat treatments routes, using different heating rates until the aging temperature and pre-aging before the aging heat treatment. The main techniques used in the characterization stage were: optical microscopy, scanning electron and transmission electron microscopy, Vickers hardness measurements and tensile and compression tests. The results indicated that the substitution of vanadium with niobium element did not modify the main characteristics of the Ti-5553 alloy, particularly the high mechanical strength and low kinetics of phase transformation. It was concluded that heat treatments performed under reduced heating rates favor the fine precipitation of the ? phase, whereas higher heating rates resulted in the growth of needles in the ? phase, influencing the mechanical behavior of the samples. It was also observed that the application of pre-aging heat treatments resulted in higher mechanical strength levels if compared to direct aging treatments. The replacement of V with Nb promoted slight increase in ductility. However, application of different heat treatments did not alter the fracture mechanisms, classified as quasi cleavage, or cleavage with dimplesMestradoMateriais e Processos de FabricaçãoDoutor em Engenharia Mecânica33003017CAPE

Effects of double-aging heat-treatments on the microstructure and mechanical behavior of an Nb-modified Ti-5553 alloy

Ti-5553 and related alloys are known as important structural alloys in the aircraft industry. In this work, the effect of double aging heat-treatments on the phase transformations and mechanical behavior of an Nb-modified Ti-5553 alloy (Ti-12Nb-5Al-5V-3Cr-0.5Fe wt%) was investigated by X-ray diffraction, scanning, and transmission electron microscopy. Results show the phase transformation sequence is altered with the time spent at the first aging stage. After 3 h at 350 degrees C, isothermal omega-phase is extensively formed throughout the beta-matrix, while after 8 h, alpha-phase embryos were detected. The first stages of alpha-phase formation in the modified alloy seem to be influenced both by the presence of omega particles and low-angle grain boundaries. Microstructures resultant of the first stages of aging change the response to the second stage, performed at 525 degrees C and 600 degrees C, for 2 h. The final microstructure obtained for the modified alloy (Ti-12Nb) after the second stage of aging diverge from the original Ti-5553 alloy subjected to the same heat-treatment. Finally, tensile and compression tests indicate Ti-12Nb is a viable substitute for Ti-5553, with comparable strength and slightly lower ductility after double aging743716725FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP14/24449-0; 16/22714-

α phase precipitation and mechanical properties of Nb-modified Ti-5553 alloy

Metastable β Ti alloys can be strengthened by controlling α phase precipitation during aging heat treatments. An example of this is Ti-5553 alloy (Ti-5Al-5Mo-5V–3Cr-0.5Fe wt%), which has been extensively applied in the aerospace industry due to its high strength-to-weight ratio. The substitution of V with Nb in Ti-5553 enhances the alloy's hardenability and may alter the mechanisms of α phase precipitation, thereby affecting its mechanical properties. Accordingly, the aim of this study was to evaluate the α phase precipitation and mechanical behavior of Nb-modified Ti-5553. Samples were prepared by arc melting and hot working by swaging, and then subjected to HT1 (solution heat-treated above β transus and aged at 600 °C for 600 min) or HT2 (heat-treated at temperatures below β transus, air cooled, heated to 600 °C and aged for 600 min). Compared to the base Ti-5553, the Nb-modified alloy exhibited improved mechanical strength in the HT1 condition due to nonhomogeneous α phase precipitation, but lower ductility in both aging conditions. An examination of the fracture surface revealed that the substitution of V with Nb did not change the fracture behavior and all the samples showed a quasi-cleavage fracture mode with some evidence of intergranular features. The Ti-5553 samples subjected to HT1 presented more dimples and hence, higher ductility. On the other hand, the HT2 samples showed fracture surfaces with predominantly transgranular features. Lastly, with regard to the pseudospinodal mechanism in the Nb-modified alloy, it was found that the substitution of V with Nb reduces the temperature at which pseudospinodal decomposition occurs by roughly 75 °C670112121CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPNão temNão temThe authors gratefully acknowledge the Brazilian research funding agencies FAPESP (São Paulo Research Foundation) and CNPq (National Council for Scientific and Technological Development) for their financial support, CBMM Co. for supplying Nb, and Prof. Hamish L. Fraser for the use of the FIB/TEM facilities at CEMAS/Ohio State Universit

Crystallographic features of the Al3Nb, Nb2Al and Nb(Ni-1 (-) Al-x(x))(2) phases in a directionally solidified ternary eutectic microstructure

Under directional growth, the eutectic transformation L reversible arrow Al3Nb + Nb2Al + Nb(Ni(1-x)Alx)(2) resulted in a very organized three phase microstructure. While many features of this eutectic have already been explored, crystal-lographic details of its phases are still missing. This paper aims to investigate composition and crystallographic features of a directionally solidified eutectic made up of the Al3Nb, Nb2Al and Nb(Ni1-xAlx)(2) phases. It was observed that the Nb(Ni1-xAlx)(2) intermetallic phase has the C14 structure, with composition 56.91 +/- 0.43 at.% Al, 10.11 +/- 0.12 at.% Ni and 32.98 +/- 0.53 at.% Nb. Selected area diffraction in a transmission electron microscope permitted interplanar spacings to be determined and values obtained are consistent with those in the literature. Accurate lattice parameters were determined using powder X-ray diffraction combined with Rietveld refinement. It was found that the lattice parameters of the Nb(Ni1-xAlx)(2) (x = 0.85) phase are a = 5.031 angstrom and c = 8.298 angstrom and these lattice parameters depend on Al content147303310CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP209449/2013-62013/50391-