Kátia Cristiane Gandolpho Candioto

Characterization of the Superalloy Inconel 718 After Double Aging Heat Treatment

The application of heat treatment, by solid solution and precipitation hardening, is very important to optimize the mechanical properties of superalloys. The main phases present in Inconel 718 are: gamma prime γ′ face ordered Ni3(Al, Ti); gamma double prime γ″ bct ordered Ni3Nb; eta η hexagonal ordered Ni3Ti; delta δ orthorhombic Ni3Nb intermetallic compounds and other topologically closed-packed structures such as μ and Laves phases. δ, μ and Laves phases have low ductility, which causes losses in mechanical and corrosion properties (Fu et al. in Mater Sci Eng A 499:215–220, 2009 [1]). The heat treatment applied to Inconel 718, precipitation hardening, has two steps: solid solution and aging treatment. In first step the secondary (hardening) phases are dissolved along the matrix, as well as carbides. It is important to note that after 650 °C (Durand-Charre in The microstructure of superalloys. CRC Press, Boca Raton, 1997 [2]) and with long exposure times, γ″ transforms in the stable phase δ, which results in a loss of mechanical resistance. In this study we aim to characterize the microstructure and phases in superalloy Inconel 718 during the steps of heat treatment with double aging. The double aging treatment performed followed the steps of solid solution to 1095 °C/1 h and double aging at 955 °C/1 h to 720 °C/8 h + 620 °C/8 h. The characterizations were performed through the techniques of XRD and SEM/EDS. It was possible to obtain the microstructural and phases characterizations before and after heat treatment in all steps.

Preparation and Test of Conventional Composite Abrasives Using Recycled Alumina Grains

In this work we report the preparation and evaluation of the mechanical characteristics of resin-bond composite abrasives using virgin and recycled alumina grains. The composite abrasives were made with phenolic resin as binder and as-received virgin and recycled alumina grains. Three different recycled alumina grains were studied: i) alumina from wood firing resin-bond abrasive tools; ii) alumina from wood firing vitrified-matrix abrasive tools; and iii) ground alumina from vitrified-matrix abrasive tools. The virgin alumina grains were employed in order to compare the mechanical performance of the prepared composite abrasive. The composition of alumina grains, analyzed by X-ray fluorescence spectroscopy revealed the recycled alumina grains have lower alumina content and higher concentration of silica in vitrified-matrix abrasives samples. The sand blast penetration tests have shown lower penetration depth in the virgin and the ground vitrified-matrix grains composites. The impact strength test results revealed its dependence on the alumina and silica content: samples with higher alumina content present the higher impact resistance whereas samples with higher silica content present lower impact strength.

Effect of Aging Treatment on Inconel 718 Superalloy: Application in Elevated Temperatures

This work studies the effect of double aging heat treatment on superalloy Inconel 718. The heat treatment followed two steps: Solid solution at 1095oC for 1h, and two steps of aging 955oC/1h - 720oC/6,5h - 720oC/1,5h + 620oC/8h. Parameters such as grain size, secondary phases distribution and qualitative analysis via SEM/EDS and Vickers hardness are used in order to evaluate the microstructural evolution. The results show increase of grain size and Vickers hardness, as well as a better distribution of secondary phases along the matrix.

Study of the Secondary Phases in Inconel 718 Aged Superalloy Using Thermodynamics Modeling

The evaluation of stability of secondary phases in superalloys is of great importance because of its application under high homologue temperatures. The precipitation hardening Inconel 718 superalloy has high stress rupture and creep resistance, good LCF behavior and high corrosion resistance. Those properties can be obtained due to the high stable matrix based on Ni, Fe and Cr, as well as secondary phases promoters elements such as Ti, Al and Nb. This study aims to analyze the phase stability among a range of temperature from 500°C to approximately 1400°C. The thermodynamic modeling has a high importance to predict the behavior of alloys among equilibrium transition. The microstructure of the system was evaluated using Thermo-Calc software and the selected databases: SSOL4 and TTNI6. This analysis made possible the prediction of the phases presented, compositions and amounts. Results from SEM analysis were used to compare the results obtained, showing good coherence between them.