Purpose: The thermal diffusivity variation of UNS S32304 duplex stainless steel welds was studied after pulsed GTA welding autogenous process without filler addition. This property was measured in the transverse section of thin plates after welding process and post-heat treated at 750°C for 8 h followed by air-cooling. Design/methodology/approach: The present work reports measurements of thermal diffusivity using the laser-flash method. The thermal cycles of welding were acquired during welding by means of k-type thermocouples in regions near the weld joint. The used shielding gas was pure argon and 98% argon plus 2% of nitrogen. The temperature profiles were obtained using a digital data acquisition system. Findings: It was found an increase of thermal diffusivity after welding process and a decrease of these values after the heat treatment regarding the solidified weld pool zone, irrespective of the welding protection atmosphere. The microstructure was characterized and an increase of austenite phase in the solidified and heat-affected zones was observed for post-weld heat-treated samples. Research limitations/implications: It suggests more investigation and new measurements about the influence of the shielding gas variation on thermal diffusivity in the heat-affected zone. Practical implications: The nuclear industry, especially, requests alloys with high thermal stability in pipes for power generation systems and safe transportation equipment’s for radioactive material. Thus, the duplex stainless steel grades have improved this stability over standard grades and potentially increase the upper service temperature reliability of the equipment. Originality/value: After heat treatment, the welded plate with 98%Ar plus 2%N2 as shielding gas presented a thermal diffusivity closer to the as received sample. By means of 2%-nitrogen addition in shielding gas during GTAW welding of duplex stainless steel may facilitate austenite phase reformation, and then promotes stability on the thermal diffusivity of duplex stainless steels alloys.

The main thermal properties of ceramics with double perovskite structure were investigated by relating these properties with their microstructural characteristics. The results define important parameters on the durability at high temperatures, creep resistance and greater understanding of heat transport in porous media. The samples Ca2MnReO6 and Ca1.8Ce0.2MnReO6 repaired using the technique of solid state reaction were studied here. Images obtained by scanning electron microscopy made it possible to evaluate the average size of junctions between grains. To evaluate this average particle size was carried out a statistical survey of the size of the junctions between grains. Taking the histograms produced, it was fitted a curve of a statistical gamma distribution density range. We observed that Ca2MnReO6 showed greater average size of junctions. The Laser Flash method was used to study the thermal diffusivity. A low value of thermal diffusivity equal to (0,27 ± 0,09).10−7 (2 /) for sample undoped and a 5-fold higher value for doped with cerium sample was observed. This difference was associated with high porosity and a larger average size of the junction to Ca2MnReO6 sample.

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Introduzido por Parker em 1961, o método do pulso de energia (Método Flash) é a mais usada e mais conhecida técnica para a determinação da difusividade térmica de materiais cerâmicos. Consiste de um método direto na determinação da difusividade térmica, no qual um pulso de energia radiante e de curta duração é incidido sobre uma das faces da amostra, sendo medida a variação de temperatura na face oposta. Este estudo tem o objetivo de descrever de forma explícita o caminho adotado por Parker para elaboração deste método. Partindo da equação de Difusão de calor, obtém-se a solução da equação diferencial parcial com condições de contorno não homogêneas, que fornece a relação da difusividade térmica com a largura da amostra e com o tempo para que o aumento de temperatura na face oposta a aplicação do feixe seja a metade do valor máximo.