Estudio del efecto de las tensiones aplicadas y la orientación cristalográfica sobre la precipitación de hidruros en aleaciones base Ti

Abstract

Tesis para optar al título de Magister en Ciencia y Tecnología de Materiales

El presente trabajo tiene por objetivo determinar la tensión umbral de reorientación de los hidruroa, durante la precipitación, en muestras de a-Ti de grano grande. En este estudio se tuvo en cuenta el efecto de la orientación cristalográfica de los granos en relación con las tensiones actuantes. Por tal motivo, se realizaron sucesivos ensayos de precipitación de hidruros bajo carga constante, en condiciones de enfriamiento lento, a partir de 260 grados C y con niveles crecientes de carga. Para lograr el objetivo del trabajo se maquinaron probetas de tracción a partir de placas de Ti puro que habían sido sometidas a un tratamiento térmico de crecimiento de grano. La orientación cristalina de los granos se determinó usando las técnicas de Laue y de Kossel. Se incrementó el contenido de H en las probetas a partir de ensayos de carga catódica. La observación de los hidruros precipitados en las probetas se realizó con microscopía óptica bajo luz polarizada. Se obtuvo la distribución de orientaciones de los hidruros en las probetas sin la carga aplicada y con distintos niveles de carga impuesta a las mismas. Del estudio realizado se concluye que el nivel umbral de tensión para la reorientación de hidruros en alfa-Ti es de aproximadamente 26 MPa. Por último se señala que aquellos planos que se encuentran más próximos a ser perpendiculares al eje ténsil se ven favorecidos para la precipitación de hidruros. Si además ese plano corresponde a un prismático, el efecto de reorientación se ve aumentado.|The objective of the present study is to determine the hydrides reorientation threshold stress during their precipitation in large grains of titanium samples. The effect of the crystallographic orientation related to the applied stress was taken into account in the present study. Successive hydrides precipitation tests with constant load applied were done, during slow cooling condition from 260 C degree and with increasing load levels. In order to reach the objective of this study, tensile stress specimens were manufactured using commercial grade pure Ti plates, with large grains. The crystallographic orientation of the grains was determined using the Laue and Kossel techniques. Cathodic charge tests were used to increase the hydrogen contained in the samples. The observation of the precipitated hydrides in the specimens was done with optic microscopy under polarized light. The distribution of the hydrides orientations in the specimens was obtained without applied load and with different load levels imposed. This study showed that the hydrides reorientation threshold stress in alpha Ti is approximately 26 Mpa. Finally, those planes closest to a perpendicular to the tensile axe position are favored for the hydrides precipitation. Moreover, if this plane corresponds to a prismatic, the effect of reorientation is increased.

The objective of the present study is to determine the hydrides reorientation threshold stress during their precipitation in large grains of titanium samples. The effect of the crystallographic orientation related to the applied stress was taken into account in the present study. Successive hydrides precipitation tests with constant load applied were done, during slow cooling condition from 260 C degree and with increasing load levels. In order to reach the objective of this study, tensile stress specimens were manufactured using commercial grade pure Ti plates, with large grains. The crystallographic orientation of the grains was determined using the Laue and Kossel techniques. Cathodic charge tests were used to increase the hydrogen contained in the samples. The observation of the precipitated hydrides in the specimens was done with optic microscopy under polarized light. The distribution of the hydrides orientations in the specimens was obtained without applied load and with different load levels imposed. This study showed that the hydrides reorientation threshold stress in alpha Ti is approximately 26 Mpa. Finally, those planes closest to a perpendicular to the tensile axe position are favored for the hydrides precipitation. Moreover, if this plane corresponds to a prismatic, the effect of reorientation is increased.