Laser Deposition Experiments Research Articles

A solidification mode selection process map for laser powder bed fusion additive manufacturing of B-modified Ti6Al4V

The unique solidification kinetics of laser powder bed fusion (LPBF) additive manufacturing tend to result in solidification modes deviating from the phase diagram predictions. This study documents an approach for developing LPBF solidification mode selection process map based on an analytical equation model which determines the solidification mode transition criteria as a function of laser power ( P ), scan velocity ( V ) and material properties. As case studies, solidification mode selection process maps were developed for three Ti6Al4V-xB alloys (x = 1, 2, 5 wt% B), presenting primary β , primary TiB, and coupled eutectic solidification modes. To validate the proposed approach, laser deposition experiments were conducted to fabricate single-tracks, single-layer and two-layer pads on arc-melted Ti6Al4V-xB alloy buttons with different P-V parameters. The model-developed process maps agreed with the experimental results. P-V windows were found to allow coupled-eutectic solidification for off-eutectic Ti6Al4V-1, 2, 5 % B and primary- β solidification for hyper-eutectic Ti6Al4V-5 %B, producing a microstructure with a continuous TiB network and a microstructure with a discontinuous network of nano-scale TiB whiskers respectively. Single-layer and two-layer pads showed consistent microstructure features of the tracks, except for the narrow region that was remelted during pad deposition. Melt pool hardness was measured, which increases with scan velocity and shows a sudden change when solidification mode was altered. The potential and limitations of the proposed method for LPBF microstructure investigation are discussed. • An approach based on analytical models was used to develop a solidification mode selection process map for LPBF. • Solidification process maps were constructed for LPBF of Ti6Al4V-1, 2, 5%B, showing windows for coupled eutectic mode. • By varying P-V parameters, high-B% Ti6Al4V-xB solidification alters from primary TiB to eutectic to primary β-Ti mode. • LPBF with Ti6Al4V-xB could render four TiB morphologies after solidification

Study on friction, wear and thermal insulation properties of laser deposition Ni/ZrO2

In order to study the effect of zirconia on the properties of laser deposited Ni15 coating on Q345 steel, laser deposition experiments were carried out with LSJG-GQ-6000M3 laser equipment with rated power of 6000 watts. The effects of adding zirconia on the microstructure, wear resistance and thermal insulation of the coating were studied by electron microscope, energy dispersive spectrometer, hardness tester, friction and wear tester and thermocouple. Study found that the addition of zirconia can refine the microstructure, improve the hardness and reduce the friction coefficient. The wear pattern has changed, and the high temperature resistance of the coating is improved.

Process improvement in laser hot wire cladding for martensitic stainless steel based on the Taguchi method

Laser hot wire cladding, with the prominent features of low heat input, high energy efficiency, and high precision, is widely used for remanufacturing metal parts. The cladding process, however, needs to be improved by using a quantitative method. In this work, volumetric defect ratio was proposed as the criterion to describe the integrity of forming quality for cladding layers. Laser deposition experiments with FV520B, one of martensitic stainless steels, were designed by using the Taguchi method. Four process variables, namely, laser power (P), scanning speed (Vs), wire feed rate (Vf), and wire current (I), were optimized based on the analysis of signal-to-noise (S/N) ratio. Metallurgic observation of cladding layer was conducted to compare the forming quality and to validate the analysis method. A stable and continuous process with the optimum parameter combination produced uniform microstructure with minimal defects and cracks, which resulted in a good metallurgical bonding interface.

Structural, compositional, mechanical characterization and biological assessment of bovine-derived hydroxyapatite coatings reinforced with MgF2 or MgO for implants functionalization

Hydroxyapatite (HA) is a consecrated biomaterial for bone reconstruction. In the form of thin films deposited by pulsed laser technologies, it can be used to cover metallic implants aiming to increase biocompatibility and osseointegration rate. HA of animal origin (bovine, BHA) reinforced with MgF2 (2wt.%) or MgO (5wt.%) were used for deposition of thin coatings with improved adherence, biocompatibility and antimicrobial activity. For pulsed laser deposition experiments, a KrF* (λ=248nm, τFWHM≤25ns) excimer laser source was used. The deposited structures were characterized from a physical–chemical point of view by X-Ray Diffraction, Fourier Transform Infra-Red Spectroscopy, Scanning Electron Microscopy in top- and cross-view modes, Energy Dispersive X-Ray Spectroscopy and Pull-out adherence tests. The microbiological assay using the HEp-2 cell line revealed that all target materials and deposited thin films are non-cytotoxic. We conducted tests on three strains isolated from patients with dental implants failure, i.e. Microccocus sp., Enterobacter sp. and Candida albicans sp. The most significant anti-biofilm effect against Microcococcus sp. strain, at 72h, was obtained in the presence of BHA:MgO thin films. For Enterobacter sp. strain a superior antimicrobial activity at 72h was noticed, in respect with simple BHA or Ti control.The enhanced antimicrobial performances, correlated with good cytocompatibility and mechanical properties recommend these biomaterials as an alternative to synthetic HA for the fabrication of reliable implant coatings for dentistry and other applications.

Design and performance of a ZnSe tetra-prism for homogeneous substrate heating using a CO_2 laser for pulsed laser deposition experiments

We report on the design and performance of a ZnSe tetra-prism for homogeneous substrate heating using a continuous wave CO(2) laser beam in pulsed laser deposition experiments. We discuss here three potential designs for homogenizing prisms and use ray-tracing modeling to compare their operation to an alternative square-tapered beam-pipe design. A square-pyramidal tetra-prism design was found to be optimal and was subjected to modeling and experimental testing to determine the influence of interference and diffraction effects on the homogeneity of the resultant intensity profile produced at the substrate surface. A heat diffusion model has been used to compare the temperature distributions produced when using various different source intensity profiles. The modeling work has revealed the importance of substrate thickness as a thermal diffuser in producing a resultant homogeneous substrate temperature distribution.

Chemical Kinetic Modeling of HMX and TATB Laser Ignition Tests

Recent high-power laser deposition experiments on octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) produced ignition times from milliseconds to seconds. Global chemical kinetic thermal decomposition models for HMX and TATB developed to predict thermal explosion experiments lasting seconds to days are applied to these laser ignition experimental data. Excellent agreement was obtained for TATB, while the calculated ignition times were longer than experiment for HMX at lower laser fluxes. Inclusion of HMX melting and faster reaction for liquid HMX in the HMX decomposition model improved the agreement with experiment at lower laser energies.

Laser ablation of ceramic oxides in the presence of a RF pulsed oxygen plasma

We have carried out laser ablation of ceramic targets with synchronous pulsed injection of molecular oxygen gas ionized and dissociated by a radio-frequency discharge. Time- and space-resolved optical absorption spectroscopy diagnostics reveals that the conditions occurring in conventional ceramic laser deposition experiments, i.e. with a continuous flow of molecular oxygen, can be recovered in the novel configuration. This approach allows us to reduce sample exposure to oxygen, which may be useful to prevent substrate oxidization in coated conductor fabrication.

Laser ablation of ceramic oxides in the presence of a RF pulsed oxygen plasma

We have carried out laser ablation of ceramic targets with synchronous pulsed injection of molecular oxygen gas ionized and dissociated by a radio-frequency discharge. Time- and space-resolved optical absorption spectroscopy diagnostics reveals that the conditions occurring in conventional ceramic laser deposition experiments, i.e. with a continuous flow of molecular oxygen, can be recovered in the novel configuration. This approach allows us to reduce sample exposure to oxygen, which may be useful to prevent substrate oxidization in coated conductor fabrication.

Possible Density Determination of the Nebular Component of Cataclysmic Variables with the N III 4641/4635 Line Ratio

The dependence of the N III 4641/4635 line ratio on the electron density is presented. It is shown that this ratio may be an important diagnostic tool in cataclysmic variables.Pérez-Tijerina, Bohigas & Machorro (2001) used the Chianti code and database developed by the U.S. Nautical Observatory (Landi, 200) in order to find density and temperature sensitive line ratios in the conditions occuring in plasmas produced in pulsed laser deposition experiments for thin film deposition, i.e., around 1018 cm 3 and 104 K. Level populations are determined considering only radiative decay and collisional excitation and de-excitation.

Extensive Studies of the Plume Deflection Angle During Laser Ablation of Si Target

The plume deflection effect during long laser irradiation of a Si target has been extensively studied. Two different laser ablation experiments were performed to study the plume deflection angle and the ablation rate versus the number of laser pulses/site. Scanning electron microscopy (SEM) analyses and profilometry of the Si target surface were performed to examine the continuous morphological changes produced by the laser irradiation. The roughening of the target surface strongly influenced the formation and expansion of the Si plume. Plume deflection angles higher than 30° have been observed by a digital camera. Complementary mass spectrometer measurements confirmed that the ion flux distribution is strongly oriented along the laser beam direction. In addition to laser ablation experiments, two other laser deposition experiments were performed: with the conventional configuration and with a new approach, termed frontal off-axis deposition. The new pulsed-laser deposition configuration provides much better control of uniformity and film thickness than the conventional deposition configuration.

Growth mechanism of YMnO3 film as a new candidate for nonvolatile memory devices

We have proposed ReMnO3 (Re: rare earth) thin films for nonvolatile memory devices. We examine the growth mechanism of YMnO3 films on (0001)ZnO:Al/(0001) sapphire substrate using rf magnetron sputtering and pulsed laser deposition methods with oxide compound target. We have succeeded in obtaining (0001) epitaxial YMnO3 films on (111) MgO and (0001)ZnO:Al/(0001) sapphire substrate, and polycrystalline films on (111)Pt/(111)MgO. For an optimal structure, the film needed much less oxygen from the gas phase compared to other oxide films. The composition (Y/Mn ratio) of the YMnO3 films changed drastically by varying the partial oxygen pressure in the sputtering gas. In addition the Y/Mn ratio slinfled with sputter time due to target surface modification, probably caused by Y segregation. An extremely small amount of oxygen is required to form the YMnO3 crystal. This was confirmed by pulsed laser deposition experiments.