High speed laser surface modification of Ti–6Al–4V

Abstract

Titanium and its alloys have been commonly used for biomedical implant applications for many years; however, associated high coefficient of friction, wear characteristics and low hardness have limited their long term performance. This article investigates the effects of the high speed laser surface modification of Ti6A1-4V on the microstructure, surface roughness, meltpool depth, phase transformation, residual strain, microhardness, and chemical composition. Laser treatment was carried out using a 1.5 kW CO 2 laser in an argon gas environment. Irradiance and residence time were varied between 15.7 to 26.7 kW/mm 2 and 1.08 to 2.16 ms respectively. Laser treatment resulted in a 20 to 50 pm thick surface modified layer without cracks. An increase in residence time and irradiance resulted in higher depth of processing. Surface roughness was found to decrease with increase in both irradiance and residence time. Metallography showed that a martensite structure formed on the laser treated region producing acicular a-Ti nested within the aged p matrix. The laser treatment reduced volume percentage of p-Ti as compared to the non-treated surface. Lattice stains in the range of 0.81% to 0.91% were observed after laser surface modification. A significant increase in micro-hardness was recorded for all laser treated samples. Microhardness increased up to 760 HV 0 . 05 which represented a 67% increase compared to the bulk material. Energy Dispersive X-ray Spectroscopy (EDS) analysis showed that laser surface modification produced a more homogenous chemical composition of the alloying elements compared to the untreated bulk metal.

In vitrofibroblast and pre-osteoblastic cellular responses on laser surface modified Ti–6Al–4V

“…The phase structure transformed from the typical α (dark regions) + β (lighter regions) structure before processing into a fine martensite structure after processing due to the low residence times used in the experiments which resulted in high cooling rates. An associated reduction in β phase from an average of 29%, in the non-laser treated material, to an average of 21%, in the laser treated material, was previously recorded via XRD [31]. No observable voids, inclusions, or pits were present.…”

“…This crack elimination is attributed to the high speed processing, ensuring minimal thermal stress exerted on the surface thus avoiding crack development. A detailed investigation of the influence of the process parameters on the surface topology has been reported previously [31]. The laser treated surfaces had average roughness values between 1.39 and 2.73 μm depending on the the process parameters, with the lower roughness values occurring at the higher irradiance values for the range of irradiance levels investigated; refer to online supplementary table S1(stacks.iop.org/ BMM/10/015007/mmedia).…”

“…In our previous work, we gained an understanding of the mechanisms of formation of surface roughness, melt pool depth, phase transformation, residual strain and chemical composition of the microstructures on Ti-6Al-4V processed via high speed laser processing [31]. The work presented in this paper is focused on an in-depth investigation of the effects of laser surface melting on in-vitro biocompatibility of Ti-6Al-4V by culturing fibroblast and osteoblast cell lines on the surfaces to determine in vitro cytotoxicity, cell viability, cell attachment, proliferation and metabolic activity.…”

Influence of Rapid Solidification on the Thermophysical and Fatigue Properties of Laser Additive Manufactured Ti-6Al-4V Alloy

“…Chikarakara et al [37] worked on the high-speed laser surface modification of Ti6Al4V. The low density, high strength to weight ratio and biocompatibility affords Ti6Al4V application in biomedical engineering.…”

Laser Surface Modification — A Focus on the Wear Degradation of Titanium Alloy

“…A technique of achieving the specified requirement is by the development of hightemperature resistance, improved hardness, and high wear-resistant coatings suitable to protect the base material against corrosion, wear, and erosion -corrosion at high temperatures. Surface modification techniques can be applied to address these limitations [16,17], such as improvement in the functionality of a solid surface by altering its chemical composition or microstructure leading to increase in the surface hardness, decrease in coefficient of friction, and enhanced wear resistance of titanium alloys without altering the desirable bulk properties of the substrate [2,14].…”