Leonardo Sales Araújo

The Effect of δ Phase on the Mechanical Properties of an Inconel 718 Superalloy

The relationship between the δ phase content and the mechanical properties of Inconel 718 superalloy is still uncertain in the scientific literature. This study investigated the effects of the amount of δ phase and of the grain size on the mechanical properties of an aged γ-matrix with γ′ and γ″ precipitates. The material in as-received condition in the form of a forged bar was solution-treated in different conditions and aged according to UNS7718 standard. The microstructures were characterized using optical, scanning, and transmission electron microscopy. Hardness and tensile tests were also conducted. After solution treatment, γ′ and γ″ phases are dissolved and δ phase volume fraction is reduced to a minimum amount only observed by TEM, resulting in an increase of the grain size and a decrease of hardness and strength. After aging, the precipitation of γ′ and γ″ occurs and the amount of δ phase increases. The volume fraction of δ phase varying from 0.30 to 1.38% and the grain size varying from ASTM 7 to 5 do not have a significant effect on the tensile properties and hardness.

Analysis of Grain Boundary Character in a Fine-Grained Nickel-Based Superalloy 718

Abstract In the current work, sheets of superalloy 718 were processed via thermomechanical route by hot and cold rolling, followed by annealing below the δ phase solvus temperature and precipitation hardening to optimum strength. Grain boundary character distribution throughout the processing was mapped via EBSD and its evolution discussed. The results show that it is possible to process the alloy to a fine grain size obtaining concomitantly a considerably high proportion of special boundaries Σ3, Σ9, and Σ27. The precipitation of δ phase presented a strong grain refining role, without significantly impairing the twinning mechanism and, consequently, the Σ3, Σ9, and Σ27 boundary formations.

Failure of a Bucket-Wheel Stacker Reclaimer: Metallographic and Structural Analyses

The structural collapse of an iron-ore bucket-wheel stacker reclaimer at the beginning of operation was investigated by means of mechanical tests, microstructural characterization, and computational structural analysis. The mechanical failure was a consequence of a brittle fracture by cleavage. The crack followed the heat-affected zone of a welded joint connecting a rectangular hollow section member and a plate flange. The main factors contributing to failure were related with a combination of design-in and manufacturing-in factors like high load–strength ratio at the point of failure, local stress concentration as a result of geometry restrictions, and weld defects. This particular section was responsible for the load transfer between the front tie member and the boom extremity, and its failure was the main cause of the catastrophic failure of the equipment.

Effect of Hot Swaging on Microstructure and Properties of Aged Ti-10Mo-20Nb Alloy

Mechanical properties of metastable β-Ti alloys are highly dependent on the final microstructure, which is controlled by the thermomechanical processing. These alloys are used for biomedical applications and require a high mechanical strength as well as a low Young’s modulus to avoid stress shielding. Previous work on the development of cold swaged Ti-10Mo-20Nb alloy showed that the best compromise strength and Young ́s modulus was obtained when the forming is followed by an aging heat treatment at 500 oC. In this work, Ti-10Mo-20Nb alloy was hot swaged and aged at 500 oC for 10 min, 4h and 24h. The microstructure was analyzed by X-ray diffraction, optical microscopy and transmission electron microscopy. Mechanical characterization was based on Vickers microhardness tests and Young’s modulus measurements. Aging at 500 oC for 10 min after hot swaging resulted in a nearly 100% β phase microstructure while aging at 500°C for 4h or 24h led to a bimodal microstructure consisting on α precipitates dispersed in the β matrix. The higher hardness to Young’s modulus ratio was obtained for the sample aged at 500 °C for 4h. This value was higher than those obtained for the Ti-6Al-4V alloy and commercially pure Ti.

EFEITO DE MÚLTIPLOS CICLOS DE SOLUBILIZAÇÃO SUB-SOLVUS DELTA E ENVELHECIMENTO NA MICROESTRUTURA E PROPRIEDADES MECÂNICAS DA SUPERLIGA 718

A liga 718 foi desenvolvida para atender aos requisitos de componentes em motores aeronauticos, pela sua excelente resistencia a fluencia ate 650°C. Em uma revisao de motores aeronauticos, os componentes podem passar por sucessivos procedimentos de reparos, porem as propriedades mecânicas sao estimadas somente no desenvolvimento do projeto. Para compreender as incertezas durante os procedimentos de reparos, que podem onerar a cadeia produtiva, o presente trabalho tem como objetivo avaliar a evolucao da microestrutura e as propriedades de tracao e microdureza, apos ser submetida a sucessivos ciclos de tratamentos termicos de solubilizacao sub-solvus (954°C/1h) e envelhecimento (760°C/5h + 649°C/1h). Os materiais forjados e fundidos, tiveram suas microestruturas observadas por microscopia otica e de varredura, com identificacao dos precipitados pela morfologia. Tambem foram realizadas medidas de tamanho de grao, ensaios de dureza e de tracao. Foi observada precipitacao da fase δ nos contornos de grao, o que manteve a estrutura refinada. Porem, houve uma crescente evolucao das particulas de fase δ com o numero de ciclos, tanto em volume quanto em tamanho medio. Consequentemente, houve uma reducao da disponibilidade de Nb para a formacao de γ”, que e a principal fase endurecedora, evidenciada pela tendencia de reducao do limite de resistencia, limite de escoamento e dureza.

Analysis of Biomimetic Surgical Clip Using Finite Element Modeling for Geometry Improvement and Biomaterials Selection

An absorbable suture clip (MU9102934-1) for surgical applications was designed based on the bite mechanism of ant Atta laevigata. In order to emulate the behavior of the ant mandible, the clip was designed to naturally fall after some time, relieving the inconvenience of the clip removal process. The structure consists of a metallic handle and an absorbable polymeric tip. This study aims to optimize its geometry and select the best biomaterials to the handle structure, by analyzing its mechanical performance using the finite element method (FEM). The biomaterials selected for the simulations of the handle were AISI 316L and AISI 420 stainless steels. FEM analysis was performed using ANSYS FE software. The stress and strain distributions for each material and geometry changes were analyzed. From the analysis performed, the clip was optimized in order to be applied in a less traumatic form.

Development of Ti-12Mo-8Nb Alloy for Biomedical Application

Several beta titanium alloys were developed for biomedical applications due to the combination of low elasticity modulus, high strength, fatigue resistance and good ductility with excellent corrosion resistance. In this regard, a new metastable beta titanium Ti-12Mo-8Nb alloy was developed, as an alternative for the traditional Ti-6Al-4V alloy, with the substitution of vanadium and aluminum for molybdenum and niobium. The objective of this work was to present the microstructural characterization and mechanical properties of the Ti-12Mo-8Nb alloy, heat treated for 1h at 950oC under high vacuum and then water quenched. The microstructure of the alloy was characterized by X-ray diffraction and optical microscopy. Vickers microhardness and nanoindentation were performed for determination of hardness, Young’s modulus and the ratio of hardness to Young’s modulus. The Ti-12Mo-8Nb microstructure consisted of β phase and the values obtained for the ratio of hardness to Young’s modulus were higher than the Ti-6Al-4V alloy.

Eletrochemical Behavior of Hot Swaged and Aged Ti-12Mo-13Nb Alloy

Recent studies have focused on the development of metastable beta-type Ti alloys with non-toxic elements such as Nb, Ta, Mo and Zr for biomedical applications. These alloys present low modulus, good mechanical compatibility and good corrosion resistance. Moreover, the processing variables can be controlled to produce microstructures with specific properties. In this regard, the objective of this work was to analyze the electrochemical behavior of Ti-13Nb-12Mo alloy hot forged and aged at 500 °C/24 h. The microstructure was analyzed by transmission electron microscopy. The corrosion tests were carried out under a NaCl solution at a temperature of 25 °C. The results showed that under the conditions studied Ti-12Mo-13Nb alloy exhibited passivation, which is desirable for corrosion resistance. Therefore the alloy is a potential alternative for the of Ti-6Al-4V used in orthopedic implants.

ANÁLISE DE TEXTURA CRISTALOGRÁFICA POR DIFRAÇÃO DE RAIOS X EM AÇOS IF COM DIFERENTES ADIÇÕES DE TITÂNIO, NIÓBIO E FÓSFORO

Os acos IF (do ingles “interstitial free”) encontram ampla aplicacao na industria automobilistica devido a sua superior estampabilidade. A textura cristalografica desenvolvida durante a laminacao de acos IF tem um papel fundamental na conformabilidade das chapas laminadas, sendo desejavel o desenvolvimento de uma forte fibra gama e fraca fibra alfa. Neste trabalho, tres tipos de acos IF, com diferentes adicoes de titânio, niobio e fosforo, foram submetidos a analise de textura cristalografica por difracao de raios X, de modo a avaliar o impacto dos tratamentos termomecânicos realizados e da variacao de composicao quimica nas orientacoes cristalograficas formadas. As texturas foram analisadas utilizando-se funcoes de distribuicao de orientacao (ODF). Os resultados das secoes de ODF foram comparados a valores anteriormente obtidos para os coeficientes de anisotropia normal e planar destes mesmos acos. A textura nas amostras laminadas de fato apresentou fibra gama intensificada e fibra alfa parcial. O aco IF-TiNbP foi o que apresentou melhor textura para estampagem profunda. No entanto, foi observada componente Goss na superficie do mesmo.

PROCESSAMENTO DE SINAIS ULTRASSÔNICOS PARA A CARACTERIZAÇÃO DE UM AÇO AUSTENÍTICO RESISTENTE AO CALOR COM DIFERENTES ESTADOS DE ENVELHECIMENTO

* Contribuição técnica ao 72o Congresso Anual da ABM – Internacional e ao 17o ENEMET Encontro Nacional de Estudantes de Engenharia Metalúrgica, de Materiais e de Minas, parte integrante da ABM Week, realizada de 02 a 06 de outubro de 2017, São Paulo, SP, Brasil. PROCESSAMENTO DE SINAIS ULTRASSÔNICOS PARA A CARACTERIZAÇÃO DE UM AÇO AUSTENÍTICO RESISTENTE AO CALOR COM DIFERENTES ESTADOS DE ENVELHECIMENTO*