Fatigue life enhancement in alpha/beta Ti–6Al–4V after shot peening: An EBSD and TEM crystallographic orientation mapping study of surface layer

Abstract The design freedom offered by additive manufacturing (AM) enables the fabrication of components with internal surfaces that are challenging to access post-manufacture. This is of concern, as the surface condition can markedly deteriorate fatigue performance. Additionally, the adaptation of surface finishing methods for AM components with topologically optimized designs can be a costly practice. It is therefore desirable to consider deploying AM parts with no or minimal surface processing for targeted applications. This requires an in-depth understanding of the formation of various types of AM surfaces, including the variation in surface condition and controlling factors, and their influence on mechanical performance. The last few years have seen significant research advances in these aspects. Ti-6Al-4V is the most extensively studied alloy for AM. The research data available now allows an informative treatment of this topic for both practical applications and future research. Using laser powder bed fusion (LPBF) of Ti-6Al-4V as a model AM − alloy system, this article examines (i) the characteristics of various types of LPBF surfaces including horizontal, vertical, inclined, upward, downward, internal isolated, and slotted surfaces; (ii) the design features and LPBF variables that affect the surface topography; (iii) the capabilities of existing post-AM surface processing methods; and (iv) the influence of AM surface topography on mechanical properties by focusing on the fatigue performance. On this basis, design considerations are recommended for AM of consistent surfaces, and priority surface-related research issues are identified. The purpose is to establish an essential knowledge base for improved commercial designs for LPBF for suitable dynamically loaded applications, with no or minimal surface processing. While centering on LPBF of Ti-6Al-4V, the insights derived are expected to be applicable to other AM processes or metallic materials.

Laser powder bed fusion additive manufacturing (LPBF-AM): the influence of design features and LPBF variables on surface topography and effect on fatigue properties

Characterization of microstructure and mechanical properties for Ti-6Al-4 V processed by rotary ultrasonic roller burnishing

Influence of structure formation and properties of bimetal produced by ultrasound-assisted explosive welding

Parametric study of multi-roller rotary burnishing process

Ultrasonic energy can promote the dislocation motion in ultrasonic-assisted machining. The phase redistribution of Ti-6Al-4V alloy will occur in ultrasonic-assisted machining with appropriate ultrasonic powers. The variations of the volume fractions of β-Ti and α-Ti influence the microhardness on the processed surface. In the present paper, various rotary ultrasonic roller burnishing experiments were conducted to investigate the ultrasonic-induced phase redistribution of Ti-6Al-4V at different ultrasonic powers. The volume fractions of β-Ti and α-Ti were measured by X-ray diffraction. SEM images of the processed surfaces were used to analyze the microstructure evolution and grain refinement of Ti-6Al-4V at various ultrasonic powers. Then, the distributions of local misorientation, texture and grain boundary were observed by EBSD. The results indicated that the microhardness approached the maximum value on the processed surface while the volume fraction of β-Ti reached its maximum value. Finally, the modified phenomenological model was applied to elucidate the relationship among the microhardness, the phase volume fractions and the grain refinement. The fitting degree for microhardness between the modified phenomenological model prediction and experimental measurement was 92.2 pct.

Luanxia Chen

Papers

Ultrasonic-Induced Phase Redistribution and Acoustic Hardening for Rotary Ultrasonic Roller Burnished Ti-6Al-4V