English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Tools annual

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Presents the access of premium content as premium feature

Premium Content

Global: Zendy Plus annual

Global: Zendy Free Plan

Introduction. Ti-6Al-4V is the most common titanium alloy. And it has been mainly used for the aircraft, because it has superior ductility and toughness while it has high strength. However, there are few studies for the fatigue crack initiation mechanism of Ti-6Al-4V. In particular, the overall relationship between fatigue crack initiation behavior and active slip planes has not been identified. Therefore, the present work considered the effects of crystal orientation on fatigue crack initiation mechanism of Ti-6Al-4V by EBSD method. Experimental methods. This study used a Ti-6.4 mass% Al-4.2 mass% V bar that forged and rolled into VAR ingot (Yield stress is 870Mpa, Tensile strength is 970MPa). Test specimens were manufactured from the longitudinal direction of the round bar by electric discharge machining. The specimen surface was subsequently polished with emery paper (ranging from #600 to #2000) and alumina powder (Baikalox 3.0 CR to 0.1 CR) and silicon dioxide (OP-S suspension) to obtain the mirror surface to allow EBSD analysis. Fatigue cracks were generated using a electromagnetic bending machine; then EBSD analysis of fatigue crack initiation site was performed to obtain detailed crystal orientation information around the fatigue crack. Fatigue crack initiation tests were performed with the electromagnetic type bending fatigue testing machine applying a maximum stress 550 MPa. The frequency of stress cycling was 15 Hz. The stress ratio of R was 0.8. We try to illustrate the SFsinΩ map based on crystal orientation information by Excel visual basic for applications in addition to the SF (Schmid factor) map which can be obtained by EBSD analysis. SFsinΩ was created to take into account the perpendicular component of the slip with respect to the surface as shown in Fig. 1, and was equal to the absolute value of product of SF and sin Ω (Ω is the angle between the specimen surface and the slip direction). Experimental results. Previous study suggested that fatigue cracks are tended to generate from primary α grains having relatively high SFsinΩ values on basal slip plane(1). However, it was not revealed that whether fatigue cracks originate from primary α grains having basal planes with the maximum SFsinΩ value or not. Thus, EBSD analysis is performed on the center of the specimen where fatigue cracks occur after the fatigue test, and we illustrate the basal SFsinΩ map in the same region. Fig. 2 from left to right shows the basal SFsinΩ map, the basal SF map, and the basal SF map around the crack observed in detail after fatigue test. As shown in Fig. 2, in addition to the crack initiation grain, we picked up the grain with the high SFsinΩ value (Grain A). We predicted that fatigue cracks would originated from Grain A because the SFsinΩ value of the crack initiation grain was 0.365, in contrast, the SFsinΩ value of Grain A was 0.371. Nevertheless, fatigue cracks didn’t generate from Grain A. Therefore, we focused on the grain size as another factor to promote the crack initiation. The grain size of the crack initiation grain was measured based on the EBSD image observed in detail after fatigue test, because this grain has much noise level around itself. As a result, the grain size of crack initiation grain was 22.2 μm and the grain size of Grain A was 16.6 μm. These results suggest that fatigue cracks are generated from the grain with the high basal SFsinΩ value and the large grain size.

The effects of microstructure on small fatigue crack initiation behavior in Ti-6Al-4V