I. Research Background: Integration of Medical Titanium Alloys with LPBF Technology

Laser powder bed fusion (LPBF) is currently the leading metal additive manufacturing technology. It can melt metal powder layer by layer, rapidly fabricate complex‑shaped components, and even enable the customization of implants tailored to a patient’s anatomical features. Personalized customization , perfectly tailored to the application requirements of the medical field. Parts produced using this technology can achieve a density of up to 99.5%, with mechanical properties comparable to those of conventionally machined components.

The one selected for this study is Ti-6Ta-1.5Zr-0.2Ru-5Cu The alloy is an α+β-type medical-grade titanium alloy:

• Copper can form Ti₂Cu precipitate phase , endowing the alloy with excellent antibacterial properties while simultaneously balancing its mechanical performance;
• Trace amounts of ruthenium significantly enhance the alloy’s corrosion resistance without altering its microstructure, making it well-suited to the complex corrosive environment within the oral cavity.
• The raw materials used in the research are Spherical atomized powder (Particle size: 10–100 μm; the experiment used the 30–60 μm range), specifically tailored for the LPBF process. Atomization powder-making technology Spherical powders exhibit excellent flowability and uniform powder spreading, which are essential for ensuring the quality of laser cladding.

Traditional LPBF process parameter optimization requires fabricating full-scale test specimens, which is material‑intensive, time‑consuming, and costly. Therefore, this study employs… Single-Track Trajectory Scanning Method By printing only a single melt track, it enables rapid screening of the process window, offering lower costs and higher efficiency—making it an effective approach for process optimization.

II. Experimental Design: Multivariate Control of LPBF Single-Track Cladding

The experiment employed the AconityMIDI printing system, using a 1 mm-thick Ti-6Al-4V disk as the substrate to prevent compositional interference between the substrate and the melted sample. The study focused on… Laser power, scanning speed, spot diameter The three core variables were subjected to testing, and two key energy metrics—line energy density (LED) and surface energy density (PED)—were introduced for a comprehensive evaluation.

1. Range of Process Parameters

The experiment comprised eight sets of gradient parameter combinations, with each set yielding five single-track melt tracks. Subsequently, metallographic sample preparation and polishing were performed to conduct microstructural characterization and phase analysis.

2. Characterization Techniques

The study comprehensively employs a variety of materials testing techniques:

• SEM/SEM-EDX : Observe the melt pool morphology and microstructure, and analyze the distribution of alloying element concentrations.
• XRD : Analyze the phase composition within the alloy;
• Electrical Discharge Machining (EDM): Complete the cutting and separation of the specimen.

III. Experimental Results and Analysis: Influence of Process Parameters on Melt Pool Quality

1. Typical defects: spheroidization and unmelted powder particles

The experiments revealed two major forming defects, both of which are directly related to the laser energy input:

• Unmelted powder : A small amount of unmelted spherical powder was observed in all samples, with particle sizes consistent with those of the feed atomized powder. As the scanning speed increases and the energy input decreases, the number of unmelted particles rises.
• Spheroidization defect At high scan speeds, noticeable balling occurs in the melt pool, primarily due to insufficient energy density, resulting in high melt viscosity and poor fluidity, which leads to melt pool instability. This defect can cause uneven powder spreading and even damage to the equipment, making it a critical issue that must be rigorously avoided in LPBF processes.

Summary of patterns:

• Under the same spot diameter, The higher the scanning speed , the lower the energy input, the more severe the issues of spheroidization and unmelted powder;
• Under the same power and scanning speed, The larger the spot diameter , the lower the surface energy density, the greater the increase in surface roughness, and the more pronounced the spheroidization phenomenon becomes;
• Increasing laser power and reducing scanning speed can raise the energy density, significantly improving the continuity and uniformity of the melt pool; however, excessively high energy densities may readily induce internal porosity.

2. Determination of Optimal Process Parameters

Based on a comprehensive assessment of weld bead flatness, continuity, and surface quality, the study identified and screened out… Optimal Process Combination ：

Laser power: 157.5 W; scanning speed: 600 mm/s; spot diameter: 0.15 mm; linear energy density: 0.263 J/mm; areal energy density: 1.750 J/mm².

Under this parameter, the single-track melt pool is smooth and well‑formed, continuous with no obvious defects, and exhibits no severe spheroidization or significant amounts of unmelted powder, yielding the best overall forming performance.

3. Microstructural and Compositional Analysis

• Microstructure The as-cast alloy consists predominantly of acicular α‑Ti phase and a β‑Ti matrix; whereas the LPBF‑fabricated specimens, due to… Rapid solidification The grain size is finer, with the α‑Ti phase predominantly distributed at the grain boundaries; fine secondary phases precipitate within the matrix, and dendrites and nucleation sites can be clearly observed.
• Elemental Analysis (EDX) Comparison of elemental compositions among the as-cast alloy, atomized powder, and the optimal single-track melt pool: The concentrations of Ta and Ru remain essentially stable; the Cu content in the LPBF specimens is slightly higher than that of the as-cast alloy, while the Ti and Zr contents show a slight decrease; the black spots on the specimen surfaces are extraneous contaminants introduced during processing, not intrinsic phases of the alloy.
• Phase analysis (XRD) The XRD pattern of the optimal single-track melt pool indicates that the alloy primarily comprises α-Ti solid solution, β-Ti solid solution, and the Ti₂Cu phase Among them, the Ti₂Cu phase is the core phase responsible for the alloy’s antibacterial properties; Ta, Zr, and Ru are fully dissolved in the titanium matrix, with no independent phases formed.

IV. Research Conclusions

• Adopt Single-Track Trajectory Scanning Method It can efficiently perform the screening of LPBF process parameters for Ti‑6Ta‑1.5Zr‑0.2Ru‑5Cu alloy, offering greater cost-effectiveness and efficiency compared with conventional specimen preparation methods.
• The optimal LPBF process parameters for this medical-grade titanium alloy were determined as follows: laser power of 157.5 W, scanning speed of 600 mm/s, and spot diameter of 0.15 mm, corresponding to a linear energy density of 0.263 J/mm and an areal energy density of 1.750 J/mm².
• The rapid solidification characteristics of LPBF significantly refine the alloy’s grain structure, resulting in a microstructure dominated by α‑Ti, β‑Ti solid solution, and the Ti₂Cu phase, while preserving the alloy’s intrinsic antibacterial and corrosion‑resistant properties.
• Excessive scanning speed and an overly large spot diameter reduce the energy density, leading to defects such as balling and unmelted powder; conversely, excessively high energy density can readily cause porosity. In practical production, it is essential to tightly control the energy range.

This study provides a reliable process basis for the laser additive manufacturing of this novel antibacterial and corrosion‑resistant medical titanium alloy, and also lays an experimental foundation for the industrial-scale fabrication of personalized dental and orthopedic implants.

Image and Text Guide

Figure 1. SEM-BSE images of the as-cast Ti-6Ta-1.5Zr-0.2Ru-5Cu alloy (in mass percent), showing the microstructure within a single grain: the acicular (αTi) phase (dark), the βTi matrix phase (medium), and the Ti₂Cu phase (light) [7].

Table 1. Print envelope parameters for a single trajectory.

Figure 2. Photograph of a Ti‑6Al‑4V substrate disk, on whose surface eight LPBF square regions are distributed; each region supports a horizontal single track. The figure clearly shows the direction of argon gas flow, the melting process, and the orientation of the re‑coating procedure.

Table 2. Printing parameters for a single trajectory.

Figure 3. SEM–BSE images show the morphology of a single track under constant laser power (157.5 W), beam diameter (0.15 mm), and scanning speeds of (a) 600 mm/s, (b) 800 mm/s, (c) 1000 mm/s, and (d) 1200 mm/s; white circles indicate spherical structures.

Figure 4. SEM-BSE images show the morphology of a single track at laser powers of 315 W, beam diameters of 0.08 mm, and scanning speeds ranging from (a) 600 mm/s to (d) 1200 mm/s.

Figure 5. SEM-BSE images showing the morphology of single tracks at a constant laser power of 280 W and a scanning speed of 1200 mm/s, for different beam diameters: (a) 0.15 mm; (b) 0.22 mm; (c) 0.29 mm; (d) 0.3 mm.

Figure 6. SEM–BSE micrograph at high magnification showing the optimal single grain boundary structure of Ti‑6Ta‑1.5Zr‑0.2Ru‑5Cu (in mass percent).

Figure 7. SEM-BSE images of LPBF Ti-6Ta-1.5Zr-0.2Ru-5Cu (in mass percent), showing the αTi matrix distributed along grain boundaries and the presence of dendrites within the βTi phase.

Table 3. EDX results for the as‑received state [7], the optimal single‑layer track surface, and Ti‑6Ta‑1.5Zr‑0.2Ru‑5Cu spherical particles (in mass percent)

Table 4. EDX results for the darkest spot on the optimal single orbit of Ti-6Ta-1.5Zr-0.2Ru-5Cu (in mass percent).

Figure 8. XRD pattern of the optimal single-phase alloy Ti-6Ta-1.5Zr-0.2Ru-5Cu (in mass percent).