RESUMO O objetivo deste trabalho foi avaliar o efeito da aplicação de tratamento térmico de alívio de tensão (TTAT) e das temperaturas de preaquecimento e de interpasse sobre a microestrutura, presença de zonas parcialmente diluídas (ZPD), a microdureza e o gradiente de composição ao longo da interface de depósitos da liga AWS E NiCrMo 3 sobre os aços AISI 8630M e AISI 4130 aplicados por dois processos de soldagem (GMAW e PTA-P). Para isto foram executadas camadas sobrepostas de cordões de solda, utilizando diferentes temperaturas de preaquecimento e de interpasse. Os processos de soldagem utilizados foram os processos MIG e Plasma Pó (PTA-P). Em seguida, as interfaces dos depósitos foram submetidas às análises de composição química via EDS, às análises metalográficas por via ótica e eletrônica e a ensaios de microdureza O aumento da temperatura de preaquecimento e de interpasse resultou em maior refino dos grãos da zona termicamente afetada dos aços (ZTA) do primeiro passe, em um aumento da microdureza na ZTA, e em uma maior migração de Fe do substrato para a camada aplicada. Foi verificada uma menor diversidade e frequência de incidência de ZPD nos depósitos executados pelo processo Plasma Pó, enquanto que nos depósitos executados com o processo MIG foram encontradas ZPD do tipo descontínua, com diferentes morfologias. A aplicação do TTAT resultou em redução significativa nos valores de microdureza em todos os casos.

ABSTRACT The objective of this study was to evaluate the effect of the preheating and interpass temperature, as well as to evaluate the effect of the application of stress relief heat treatment on the microstructure, microhardness and composition gradient along the interface of AWS E NiCrMo3 alloy on AISI8630M and AISI4130 quenched and tempered steel, applied by two welding process. For this superimposed weld beads using different preheat and interpass were applied using MIG and Plasma Transfered Arc – Powder (PTA-P) welding process. The interfaces deposits were subjected to analysis of chemical composition by EDS, to metallographic examination by optical and electronic microscopy and to microhardness tests. The increase in preheat and interpass temperatures resulted in greater grain refinement of the first pass, increase of heat affected zone microhardness and in a greater Fe migration from the substrate to the applied layer. A minor frequency diversity and a lower incidence of partially diluted zones (PDZ) was observed in deposits performed by PTA-P process, where as the deposits performed with MIG process discontinuous PDZ type with different morphologies were identified. The use of stress relief heat treatment resulted in a significant reduction in microhardness values in all cases.

This paper presents a thermal and microstructural characterization of Cu87-xAl13Nbx (wt%) high temperature shape memory alloys (HTSMA), with Nb contents ranging from 1 to 3%. The alloys were obtained by arc melting under argon atmosphere. Thermal characterization was performed by differential scanning calorimetry (DSC), revealing that the phase martensitic transformation of all the studied alloys occurs in the range of 200 ºC to 450 ºC. Thermal cycling in this temperature range caused the martensitic transformation to disappear after approximately 6 cycles. However, a new heat treatment at 850 ºC followed by water quenching causes the martensitic transformation to be recovered. Microstructural characterization was performed using optical microscopy (OM) and scanning electron microscopy (SEM), revealing the presence of Nb precipitates in a Cu-Al martensitic matrix, mainly in the Nb-rich compositions. These different microstructures with Nb particles cause a hardness variation that initially decreases between 0.5 %Nb (275HV) and 1.0 %Nb (225HV), then increasing continuously up to 3.0% Nb (380HV).