Estudo de juntas soldadas a laser de chapas finas de liga com memória de forma NiTi austenítica

Abstract

ResumoLigas com memória de forma (LMF) de NiTi são materiais inteligentes que possibilitam o desenvolvimento de diversas aplicações de engenharia devido suas propriedades funcionais chamadas de efeito de memória de forma e superelasticidade. No entanto, fabricar componentes com geometria complexa a partir destes materiais é um desafio tecnológico que poderá ser superado com o desenvolvimento de técnicas efetivas de união destas ligas por soldagem. Objetivou-se neste trabalho avaliar os efeitos dos diferentes parâmetros de soldagem nas propriedades mecânicas de juntas soldadas obtidas de chapas finas de uma LMF de NiTi austenítica. As soldagens foram realizadas pelo processo de soldagem à laser (LBW -Laser Beam Welding) variando a potência e velocidade de soldagem e a realização ou não do tratamento térmico pós-soldagem (TTPS). Como ferramenta de otimização foi utilizado um planejamento experimental 2 3 e a metodologia da superfície de resposta. Foi observado que o TTPS promoveu a estabilização de um estado misto de fases na chapa de NiTi, entre a fase R e a austenita à temperatura ambiente e que após a soldagem foi possível observar uma redução dos valores aferidos de dureza no metal de solda (MS). Além disso, as juntas soldadas com velocidade de soldagem de 900 mm/min e que foram submetidas ao TTPS apresentaram resistência mecânica à tração satisfatória independentemente da potência empregada. Palavras-chave:Ligas com memória de forma, Ligas de NiTi, Processo de soldagem a laser. AbstRActNiTi shape memory alloys (SMA) are smart materials that enable the development of various engineering applications due to their functional properties called shape memory effect and superelasticity. However, to manufacture components with complex geometry from these materials is a technological challenge that can be overcome with the development of effective joint techniques of these alloys by welding. The objective of this work was to evaluate the effects of the different welding parameters on the mechanical properties of welded joints of thin sheets of austenitic NiTi SMA. The joints were performed by the laser welding process varying the power and speed of welding and the influence of post-weld heat treatment (PWHT) was verified. As an optimization and evaluation tool, a design of experiments and the response surface methodology were respectively used. It was observed that the PWHT promoted the stabilization of a phase mixed state in the thin sheet, between the R phase and the austenite at room temperature and that after welding it was possible to observe a reduction of the average values of hardness in the weld metal (WM). Furthermore, welded joints with welding speed of 900 mm/min and were submitted to PWHT showed satisfactory tensile mechanical strength independent of the welding power used.

Nickel-Titanium Alloys Welding of Thin Sheets Using GTAW: Comparative Study Between Similar and Dissimilar Welding with AISI 304 Stainless Steel

“…Therefore the PWHT could be a viable tool to manage the NiTi-NiTi rigidity and enhance its ductility. This mechanical behavior result for similar NiTi joints can be compared with those reported in the literature: Melo et al 22 using factorial experiment were able to achieve NiTi-NiTi welded joints by laser with UTS of 682 MPa as (UTS = 134MPa) 11 and (UTS ~200MPa) 8 for welding using the LBW process. This behavior is directly related to the observation of regions of high hardness in the weld metal.…”

“…The electrical resistance variation measurements were performed according to the scheme of Figure 3. This technique was chosen in detriment of the Differential Scanning Calorimetry (DSC) as it is a nondestructive technique for the determination of the phase transformation temperatures which were calculated from the tangent method 22 . The intersection of the tangent lines denotes the temperature at which the phase transformation occurs 2,23 .…”