For a non-contact, non-destructive quality evaluation, laser ultrasonic testing (LUT) has received increasing attention in complex manufacturing processes, such as additive manufacturing (AM). This work assessed the LUT method for the inspection of internal hole defects in additive manufactured Ti-6Al-4V part. A Q-switched pulsed laser was utilized to generate ultrasound waves on the top surface of a Ti-6Al-4V alloy part, and a laser Doppler vibrometer (LDV) was utilized to detect the ultrasound waves. Sub-millimeter (0.8 mm diameter) internal hole defect was successfully detected by using the established LUT system in pulse-echo mode. The method achieved a relatively high resolution, suggesting significant application prospects in the non-destructive evaluation of AM part. The relationship between the diameter of the hole defects and the amplitude of the laser-generated Rayleigh waves was studied. X-ray computed tomography (XCT) was conducted to validate the results obtained from the LUT system.

Laser polishing is a widely used technology to improve the surface quality of the products. However, the investigation on the physical mechanism is still lacking. In this paper, the established numerical transient model reveals the rough surface evolution mechanism during laser polishing. Mass transfer driven by Marangoni force, surface tension and gravity appears in the laser-induced molten pool so that the polished surface topography tends to be smoother. The AlSi10Mg samples fabricated by laser-based powder bed fusion were polished at different laser hatching spaces, passes and directions to gain insight into the variation of the surface morphologies, roughness and microhardness in this paper. The experimental results show that after laser polishing, the surface roughness of Ra and Sa of the upper surface can be reduced from 12.5 μm to 3.7 μm and from to 29.3 μm to 8.4 μm, respectively, due to sufficient wetting in the molten pool. The microhardness of the upper surface can be elevated from 112.3 HV to 176.9 HV under the combined influence of the grain refinement, elements distribution change and surface defects elimination. Better surface quality can be gained by decreasing the hatching space, increasing polishing pass or choosing apposite laser direction.

Selective laser melting (SLM) is a layer by layer process of melting and solidifying of metal powders. The surface quality of the previous layer directly affects the uniformity of the next layer. If the surface roughness value of the previous layer is large, there is the possibility of not being able to complete the layering process such that the entire process has to be abandoned. At least, it may result in long term durability problem and the inhomogeneity, may even make the processed structure not be able to be predicted. In the present study, the ability of a fiber laser to in-situ polish the rough surfaces of four typical additive-manufactured alloys, namely, Ti6Al4V, AlSi10Mg, 316L and IN718 was demonstrated. The results revealed that the surface roughness of the as-received alloys could be reduced to about 3 μm through the application of the laser-polishing process, and the initial surfaces had roughness values of 8.80–16.64 μm. Meanwhile, for a given energy density, a higher laser power produced a laser-polishing effect that was often more obvious, with the surface roughness decreasing with an increase in the laser power. Further, the polishing strategy will be optimized by simulation in our following study.

Boron-terminated bare and oxidized diamond (001) surfaces are first proposed in this paper and are modelled by adsorbing the boron (B) atoms onto the bare and oxidized diamond (001) surfaces, respectively. The electron affinities (EAs) and adsorption energies per B atom of the B-terminated bare and oxidized diamond (001) surfaces were investigated via density functional theory calculations. Applying 1 monolayer (ML) B coverage yields a more negative EA (NEA) than 0.25 ML or 0.5 ML coverage on the bare diamond surfaces, and a larger positive EA (PEA) on the oxidized diamond surfaces. Their positive adsorption energies mean that 1 ML B coverage is energetically favorable on both the bare and oxidized diamond (001) surfaces. The B-terminated bare diamond (001) surfaces with 1 ML coverage have an NEA of up to −1.39 eV, and their adsorption energy is higher than that of hydrogen-terminated diamond (001) surfaces by 1.49 eV, thus they could potentially be applied to create thermally stable electron emission devices. The B-terminated oxidized diamond (001) surfaces (1 ML coverage) have a PEA of up to 3.21 eV, larger than the EAs of ether oxidized (2.39 eV), nitrogen-terminated (3.01 eV), or fluorine-terminated (2.34 eV) diamond (001) surfaces. Consequently, the B-terminated oxidized diamond (001) surfaces show great potential for NV and SiV quantum sensing applications.