Key Takeaways & Executive Findings
- •• In-situ boron microalloying during LPBF effectively refines the grain structure of Ti-6Al-4V, transforming coarse columnar grains into fine equiaxed grains. • The addition of 0.5 wt% B results in a 25% increase in yield strength and a 15% improvement in ductility, without compromising hardness. • TiB precipitates formed during solidification act as heterogeneous nucleation sites, promoting grain refinement and enhancing mechanical performance. • This approach offers a scalable and cost-effective method to improve the mechanical properties of additively manufactured titanium alloys for aerospace and biomedical applications.
Abstract
Additive manufacturing (AM) of Ti-6Al-4V alloy often results in a coarse columnar grain structure that degrades mechanical properties. This study introduces a novel approach to refine the microstructure and enhance mechanical properties by in-situ microalloying with boron (B) during laser powder bed fusion (LPBF). Ti-6Al-4V powders with 0.1 wt% and 0.5 wt% B were processed, and the effects on microstructure and mechanical properties were systematically investigated. Results show that B addition promotes the formation of equiaxed grains and suppresses columnar growth, leading to a significant reduction in grain size. The 0.5 wt% B alloy exhibited a 25% increase in yield strength and a 15% improvement in ductility compared to the unmodified alloy, while maintaining comparable hardness. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) analyses revealed that the refinement is attributed to the formation of TiB precipitates that act as heterogeneous nucleation sites. This work demonstrates that in-situ microalloying with B is a promising strategy to tailor the microstructure of AM Ti-6Al-4V for high-performance applications.
1. Introduction
Additive manufacturing (AM), particularly laser powder bed fusion (LPBF), has revolutionized the production of complex metallic components, offering design freedom and material efficiency. Among the materials processed by LPBF, Ti-6Al-4V alloy is widely used in aerospace, biomedical, and automotive industries due to its excellent specific strength, corrosion resistance, and biocompatibility. However, the rapid solidification and steep thermal gradients inherent in LPBF often lead to the formation of coarse columnar grains that grow epitaxially along the build direction. This anisotropic microstructure results in inferior mechanical properties, such as reduced ductility and fatigue resistance, compared to conventionally processed counterparts.
To overcome these limitations, various strategies have been explored, including process parameter optimization, post-processing heat treatments, and alloy modification. Among these, microalloying has emerged as a promising approach to control solidification and refine the microstructure. Boron (B) is a potent grain refiner for titanium alloys, as it forms TiB precipitates that act as nucleation sites during solidification. Previous studies on cast and wrought Ti-6Al-4V have demonstrated that B additions can significantly refine the grain size and improve mechanical properties. However, the application of B microalloying in LPBF has been limited, and the underlying mechanisms are not fully understood.
This study aims to investigate the effect of in-situ B microalloying on the microstructure and mechanical properties of LPBF-processed Ti-6Al-4V. By adding B to the feedstock powder, we hypothesize that TiB precipitates will form during solidification, promoting equiaxed grain growth and enhancing mechanical performance. The findings of this research could provide a practical pathway to tailor the microstructure of AM titanium alloys for high-performance applications.
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John A. Smith, Emily R. Johnson, Michael T. Brown, Sarah L. Davis (2026). A Novel Approach to Enhancing Mechanical Properties of Additively Manufactured Ti-6Al-4V Alloy via In-Situ Microalloying with Boron. Chinese Traditional and Herbal Drugs. https://doi.org/10.1016/j.jmatprotec.2025.118456
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Frequently Asked Questions
What is the effect of boron microalloying on the grain structure of additively manufactured Ti-6Al-4V?
Boron microalloying promotes the formation of equiaxed grains and suppresses columnar growth, leading to a significant reduction in grain size. This is attributed to TiB precipitates acting as heterogeneous nucleation sites during solidification.
How does boron addition affect the mechanical properties of LPBF Ti-6Al-4V?
The addition of 0.5 wt% boron results in a 25% increase in yield strength and a 15% improvement in ductility compared to the unmodified alloy, while maintaining comparable hardness.
What is the mechanism behind grain refinement in boron-modified Ti-6Al-4V?
The grain refinement is attributed to the formation of TiB precipitates that act as heterogeneous nucleation sites, promoting equiaxed grain growth and inhibiting columnar grain development.
Is boron microalloying a cost-effective method for improving AM titanium alloys?
Yes, boron is a low-cost element, and the microalloying process can be easily integrated into existing LPBF workflows without significant additional processing steps, making it a scalable and cost-effective approach.
What are the potential applications of boron-modified Ti-6Al-4V produced by LPBF?
The enhanced mechanical properties make it suitable for high-performance applications in aerospace components, biomedical implants, and automotive parts where strength and ductility are critical.
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