Measurement of the grain boundary energy of commercially-pure grade 2 titanium at high temperature

Abstract

The formation of grains and their growth based on the elimination of other grains, before thermal cycles are imposed, are essential for the correct conformation of a material and to control the microstructure, texture and orientation relationships between phases. However, when the boundary of a polycrystalline grain intersects the outer surface and the material is exposed to temperatures higher than half of its fusion temperature, a crack or groove appears. This research aims to apply a method to evaluate the energy of the grain boundary (GB) and also to compare the energy values of the faces of the GB, and to investigate commercially-pure grade 2 titanium in relation to the action of forces on the grain boundary of the free surface. The thermal attack under vacuum technique was used to reveal, at high temperatures, the titanium microstructure, which is preserved under a very thin oxide layer even when the sample is brought to room temperature. Thus, at room temperature, it was possible to analyze the Ti surface viewed at high temperature. The thermal cracks or grooves appearing due to the selective vaporization of atoms at the GB were measured geometrically using atomic force microscopy. The energy relationship of the GB was determined from the microstructural appearance at high temperatures and applying the equation g gb = 2·g s ·senj to the thermal crack formed between two grains.The results were compared experimentally with others reported in the literature. With the method applied in this study it was possible to evaluate the energy of the GB and it was verified that this energy was anisotropic for the material under study.Keywords Titanium, Grain boundary energy, Atomic force microscopy, Thermal attack under vacuum. Medida de energia de contorno de grão do titânio comercialmente purograu 2 -em alta temperaturaResumo A formação e o crescimento de grãos a partir de outros existentes, perante ciclos térmicos impostos, são fundamentais para a conformação adequada do material, para controlar a microestrutura, textura e relações de orientação entre as fases. Com o princípio da formação de uma fenda térmica á partir da exposição do material a temperaturas maiores que a metade de sua temperatura de fusão, esta pesquisa visa a comprovação de um método para avaliar a energia de contorno de grão (CG), comparar os valores da energia das faces do CG e investigar a ação das forças na superfície livre dos CGs do titânio comercialmente puro grau 2. A técnica de ataque térmico sob vácuo foi empregada para revelar, em altas temperaturas, a microestrutura do titânio, esta técnica permite a manutenção da estrutura "congelada" sob uma camada de óxido de pequena espessura mesmo quando a amostra é trazida à temperatura ambiente. Com este método foi possível analisar a superfície do Ti em temperatura ambiente, como se estivesse sendo visualizada em altas temperaturas. As trincas ou fendas térmicas provenientes da vaporização seletiva de átomos no CG foram medidas geometricamente utilizando Microscopia de Força Atômica. A energia d...

Laser Assisted Size Reduction of Gold (Au) Particles onto a Titanium (Ti) Substrate Surface

“…Table 1. Chemical composition of pure titanium grade II used in experiment [24,25]. The rod was cut into 7 mm thick slices and prepared for sputtering.…”

A comparative study on fatigue indicator parameters for near‐α titanium alloys

“…ν is the Poisson's ratio, and Γ s is the surface energy considered to be 2 J/m 2 for titanium alloys. 76 The crack plane is determined based on the highest mixed-mode stress intensity factor K c ¼ T eff ffiffiffiffiffi πc p among all possible planes where dislocations activate and pierce. 3 B is the crack opening displacement, which is assumed equivalent to the displacement pile-up length and calculated as the magnitude of the net Burgers vector b.…”

“…β is the ratio between shear to normal fracture toughness of the material, which is suggested as 0.7071 in Parvatareddy and Dillard 75 for near‐ α titanium alloy. ν is the Poisson's ratio, and Γ s is the surface energy considered to be 2 J/m 2 for titanium alloys 76 . The crack plane is determined based on the highest mixed‐mode stress intensity factor among all possible planes where dislocations activate and pierce 3 .…”