Increase Of Laser Scanning Speed Research Articles

Antifouling Coatings Fabricated by Laser Cladding

Laser surface treatment is a very useful technology for the fabrication of functional surfaces. In this study, novel antifouling surfaces are fabricated by laser cladding of TC4 and Ni60 mixed materials in various mass ratios on the surfaces of 316L stainless steel substrates. Parametric studies are carried out to investigate the effects of the mixed powder mass ratios and laser cladding parameters on the antifouling performance of the laser clad coatings (LCCs). The antifouling mechanism of the LCCs is investigated by using the water contact angle/surface energy measurement, scanning electron microscope (SEM) surface observation, and phase composition analysis via XRD (X-ray diffractometer) testing. The experimental results show that the LCCs with Ni60/TC4 mass ratio of 3/7 has better antifouling performance in this study. The antifouling performance of the LCC decreases with the increase in laser scanning speed. Surface energy and surface topography have a significant effect on the antifouling performance of LCCs. In order to get the optimal antifouling performance of LCCs, the Ni60/TC4 mass ratio and laser cladding parameters should be optimized.

Enhancing the machinability of Cf/SiC composite with the assistance of laser-induced oxidation during milling

Carbon fiber-reinforced silicon carbide matrix (Cf/SiC) composites have been widely used in aerospace for its superior properties. However, due to high hardness, heterogeneity, and anisotropy, many problems such as machining damage, low process efficiency, and rapid tool wear are encountered in machining Cf/SiC composite. In this study, laser-induced oxidation-assisted milling (LOAM), as novel hybrid machining process, was proposed to enhance machinability of Cf/SiC composites. Pulsed laser was used to induce reaction between Cf/SiC composites and oxygen. Easily removable loose and porous oxides were produced, which were simultaneously removed with milling tool, leading to improved material removal rate and tool life. Oxidation mechanisms and influences of laser parameters on oxidation behavior of Cf/SiC composite were studied. Conventional milling (CONV) without the assistance of laser was also performed on Cf/SiC composite for comparative analysis. Milling force, tool wear, and surface quality were studied in detail. Under laser irradiation, Cf/SiC composite was modified into metamorphic-layer that consisted of oxide layer and transition layer. Material irradiated with laser got melted, vaporized, and then reacted with oxygen, producing oxide. Oxide layer was formed due to the accumulation of oxide. Increasing laser energy density boosted oxidation reaction and increased the thickness of oxide layer. In contrast, increase in laser scanning speed decreased thickness of oxide layer. Results show that cutting force was extremely low and no tool wear occurred during milling oxide layer, indicating significant enhancement in machinability. Abrasive wear mainly occurred on flank face when milling transition layer. Surface damages, for instance fiber fracture and matrix fragmentation, were significantly contained by LOAM. Surface roughness Sa obtained via LOAM was 9.5 μm, which was lower than that obtained by CONV (35 μm). This study indicates that LOAM can achieve high-efficiency processing, low-defect surface, and prolonged tool life when machining Cf/SiC composite.

Characterization and single track analysis of a metal-ceramic composite laser cladding over Ti6Al4V alloy

The present experimental investigation is dealt with the formation of composite cladding on Ti6Al4V alloy using laser melting and deposition (LMD) technique. The reinforcement consisting of ilmenite (Fe-TiO3), CeO2, La2O3, cubic boron nitride (cBN) and Ti6Al4V in different compositions ratio are considered as cladding materials to fabricate a dense composite clad surface. Single tracks are formed using 15.92 × 104 w/cm2 laser power density and three different laser scanning speeds of 200,400 and 600 mm/min to analyze the clad height, aspect ratio, dilution rate and average contact angle of the track. Further, area clads are fabricated for different powder compositions of the cladding materials. The clad layer thickness are found to be decreases with increase in laser scanning speed and rise in the percentage of ilmenite (Fe-TiO3). The formation of different microstructure in the clad as well as interface zone are observed. With the increase in the percentage composition of ilmenite with cerium and lanthanum leads to the refined and coarser grain microstructure with unique structure are found which enhance mechanical properties like wear and hardness of the clad. Some of the important microstructure like dendritic, lamellar, flower, grit type and long needle type are found on the clad surface. The formation of unique chemical compound such as Ti3O, La2O3, Ti2B5, LaTi21O38, Ce3B2N4, Fe4N, TiN, La3BO6, and Fe-TiO3 are observed through the XRD analysis. Micro hardness of the clad surface are found to be increases approximately five times to the substrate at the clad with the increase in percentage composition of RE element, but found to be decrease drastically as passing through the intersection zone due to intermixing phenomena of clad and the substrate. It is observed that with higher percentage composition of RE result decrease in the reduction of the coefficient of friction approximately thrice to that of the cladded sample as compare to base (Ti6Al4V), which improve the wear resistance of the clad material. However there are minor amount of defects like micro crack are found on the clad and wear at the disk are occurred due to ploughing and cutting observed through track analysis.

Effect of laser scanning speed on microstructure and mechanical properties of SLM porous Ti-5Al-5V-5Mo-3Cr-1Fe alloy

In this study, porous Ti-55531(Fe) was fabricated by selective laser melting (SLM) with different laser scanning speeds. The microstructures, surface morphology, inner defects, porosity, microhardness, and compressive behaviors were studied. The variation of lattice constant and hardness were analyzed. The results show that all the specimens have a density of ∼1 g/cm3, and a Vicker’s hardness with a range of 280–320 Hv0.1. The porosity of the SLM-produced materials is greater than the designed value (77%) and increases from 77.33% to 82.33% with the increase of laser scanning speed from 500 mm/s to 1,500 mm/s. Continuous irregular columnar dendrites, a large number of gas-induced defects with small size between 20 and 60 μm and a deep molten pool form in the specimens fabricated with a laser scanning speed less than 1,000 mm/s. Some defects, elongated voids and interrupted columnar dendrites are identified in the specimens fabricated with the laser scanning speed more than 1,000 mm/s caused by the insufficient input energy. All specimens with different laser scanning speeds show the single ß phase patterns. The compressive strength of the specimens with the laser scanning speed of 500 mm/s is maintained at 32 MPa and the compressive strength decreases with the increase of laser scanning speed. The specimens with a scanning speed of 500 mm/s present the best mechanical properties and surface quality.

Grain-based morphological simulation via fractal theory with experimental verification and corresponding optical properties in laser melting deposition additive manufacturing: A demystified approach

Laser melting deposition (LMD) stands for a challenging and promising 3D printing technology to fabricate near-net-shape parts. In this study, a 3D modified fractal model (3DMFM) has been developed by considering the surface texture orientation in the technical manufactured surfaces. Fractal parameters, including fractal dimensions and periodic lengths in the 3DMFM, have been solved for the grain-based morphologies developed by LMD. In combination with statistical parameters, these fractal parameters were applied in 3DMFM for analytical simulations. Single-track depositions of AISI 304 stainless steel powder on AISI 304 stainless steel substrate were subjected to scanning electron microscopy investigations for experimental validation of the proposed model. A customized investigational setup, having a He-Ne laser system (632.8 nm and 7.75 mW), was designed to identify the optical properties of each deposited layer. Three types of grains were identified: round quasi-continuous (RQC), elongated lath-shaped (ELS), and a combination of the two. The RQC grains were transformed into ELS grains with an increment in laser scanning speed. The RQC and ELS combination was converted into RQC grains with an increase in the powder feeding rate. RQC changed into ELS grains whenever the laser power was elevated. An increase in skewness and a decrease in kurtosis were observed whenever laser scanning speed or powder feeding rate was increased. A laser power amplification also determined a rise of skewness and a reduction in the kurtosis values. A rise in either laser scanning speed or powder feeding rate lowered the surface roughness, while an inverse correlation was observed between laser power and surface roughness. An increase in laser scanning speed or laser power increased the fractal dimensions (Dx and Dy). However, the powder feeding rate was inversely correlated with Dx and Dy. In the case of periodic lengths (Lx and Ly), the scanning speed, powder feeding rate, and laser power exhibited an inverse behavior with Dx and Dy. Larger magnitudes of Dx or Dy were resulted due to an increased optical reflection or a decreased optical absorption, while the opposite results were attained in the case of periodic lengths inclination (Lx and Ly). The developed fractal model can predict and select the best LMD process parameters in terms of quality control and time/cost-effectiveness.

Processing and Profile Control of Microhole Array for PDMS Mask with Femtosecond Laser.

Polydimethylsiloxane (PDMS) is hailed as one of the foundational materials that have been applied to different products in various fields because of its chemical resistance, low cost, excellent flexibility, and high molding capability. With the aim to achieve surface texture with high efficiency by means of electrochemical micromachining with PDMS mask, a femtosecond laser is utilized to process a precision array of micro-through-holes on PDMS films as the molds. The ablation process of PDMS with a femtosecond laser was investigated via numerical simulation verified with experiments indicating a laser energy density of 4.865 mJ/mm2 as the ablation threshold of PDMS with the melting temperature of 930 K. The spiral scanning path with optimized radial offset was developed to ablate materials from the PDMS film to form the laminated profiles, and a tapered through hole was then formed with multilayer scanning. The profile dimension and accuracy were examined as control targets in terms of laser pulse energy and scanning speed, showing that a 12 μJ femtosecond laser pulse energy and 1000 mm/s scanning speed could bring about a nearly circular laminating profile with expected smaller exit diameter than the entry diameter. All the cross-section diameters of the microcone decreased with the increase of laser scanning speed, while the taper increased gradually and then saturated around a laser scanning speed of 800 mm/s due to the energy absorption resulting in smaller ablation in diameter and depth.

Effects of laser scanning speed and building direction on the microstructure and mechanical properties of selective laser melted Inconel 718 superalloy

This work focused on the effects of different scanning speeds and building directions on the microstructure, mechanical properties, and texture of Inconel 718 parts manufactured by selective laser melting (SLM). The microstructure evolution, including orientation texture and precipitate distribution, was studied by electron backscatter (EBSD) and scanning electron microscope (SEM), and the phase was analyzed by X-ray diffractometer (XRD). The results show that with the increase of laser scanning speed, the width-to-depth ratio of single molten pool increases, and the epitaxial growth is restricted, which leads to a decrease in the intensity of the <001> texture and a decrease in the anisotropy of mechanical properties. The grain refinement caused by the increase in scanning speed further weakens the anisotropy of mechanical properties. This work can provide potential guidance of high laser scanning speed in benefiting a more homogenous microstructure and a higher production rate for SLM manufacturing.

Additive manufacturing of novel ferritic stainless steel by selective laser melting: Role of laser scanning speed on the formability, microstructure and properties

Novel ferritic stainless steel was successfully fabricated by selective laser melting (SLM) technology. This study was dedicated to the effect of laser scanning speed on the formability, microstructural evolution, wear and corrosion performance of SLM novel stainless steel. The results showed that the densification level of the SLM specimens was significantly improved with the increase of laser energy density due to the reduction in pore defects. The microstructure of the SLM specimens was mainly composed of α-Fe, with a small amount of Cr23C6. The EBSD pattern of the SLM specimens showed anisotropy due to complex thermal convection in the SLM process. The proportion of the LAGBs and α-Fe increased with the increase of laser scanning speed while the average grain size decreased from 0.481 to 0.467 μm. The SLM specimens possessed excellent properties, with the corrosion resistance significantly higher than that of some common engineering alloys. The best SLM specimen possessed a corrosion potential of −148 mV SCE, a corrosion current density of 1.38 × 10−7 A cm−2, microhardness of 812 HV, and a specific wear rate of 1.99 × 10−6 mm3/Nm.

Influence of laser scanning speed on the formation property of laser brazing diamond coating

The pre-placed BNi-2 alloy solder was utilized as braze material to fabricate brazing diamond coating on 65Mn steel substrate by using fiber laser with 5 mm × 5 mm square laser spot. The laser spot was scanned at a steady power of 1.1 kW. The effect of laser scanning speed on the formation mechanism was investigated. Different scanning speed leads to different heating conditions of solder layer, and finally leads to different melting behavior of the coating. At the small laser scanning speed (1 mm/s and 2 mm/s), the solder can be fully melted to form a small liquid ball owing to the long interaction time, and the small ball can quickly flow into the left liquid molten pool because of the high heating temperature and good fluidity. Because of its small mass, the diamond particles float on the surface of the molten pool and gather on the top of the molten pool. With the cooling and solidification of the molten pool, the diamond particles are finally fixed on the top of the coating. With the increase of laser scanning speed (3 mm/s), the solder which has not been completely melted will flip the coating toward the liquid molten ball due to the greater melting imbalance in the solder area. The initial liquid molten balls constantly gather and grow in size and finally contact with the molten pool and merge into it. However, when the scanning speed reaches 4 mm/s, the solder cannot be fully melted due to the shortening of the irradiation time of the laser spot. The graphitization degree of diamond, the exposed height of diamond and the width of coating were also studied and they are related to the previous formation process.

The effect of laser scanning speed on microstructural evolution during direct laser deposition 12CrNi2 alloy steel

This paper focused on the effect of different laser scanning speed (4 mm/s, 5 mm/s, 6 mm/s and 7 mm/s) on the microstructural evolution of direct laser deposition (DLD) 12CrNi2 alloy steel, and analyzed the relationship between microstructure and performance of DLD-processed samples. The results showed that the microstructure in the middle of as-deposited samples consisted of a large amount of bainite, a small amount of martensite (M) and ferrite (F). With the increase of laser scanning speed, the fraction of ferrite decreased from 55.6% to 14.7%, while that of martensite increased from nearly 0% to 4.9%. Besides, as increasing the laser scanning speed, granular bainite (GB) transformed into lath bainite (LB) due to the increase of cooling rate, and the fraction of LB reached the maximum of 29.9% when the scanning speed was 7 mm/s. In addition, the functions about the relationship between laser scanning speed and phase fractions were fitted in order to provide a theoretical basis for the design of DLD process parameters. EBSD maps of as-deposited samples exhibited anisotropy due to the complex heat flux direction during the multi-layer laser deposition process. With the increase of laser scanning speed, the grain size showed a downward trend from 5.89 µm2 to 3.44 µm2. The sample fabricated at 7 mm/s contained more LB and M, leading to the highest mean microhardness of 355 ± 6 HV0.2. The sample fabricated at 6 mm/s exhibited the best wear resistance due to its optimum combination of hardness and toughness. Because of a large amount of ferrite with optimal toughness, the sample fabricated at 4 mm/s had the best impact toughness of aku = 80 J/cm2.

Ultrahigh-performance TiNi shape memory alloy by 4D printing

For additively manufactured components, it's widely accepted to have high enough energy input to facilitate nearly full density and low enough energy input to avoid cracking tendency. In this work, ultrahigh-performance Ti50.6Ni49.4 (at.%) shape memory alloy (SMA) was manufactured by selective laser melting (SLM) under high enough energy inputs (155–292 J/mm3). The microstructure, phase transformation behaviors, mechanical and shape memory properties of the SLM-manufactured SMA were investigated by various characterization methods of X-ray diffraction, scanning and transmission electron microscopies, differential scanning calorimetry, room temperature and stress-controlled cyclic tensile tests, etc. Results show that the martensite content and the austenite and martensitic transformation temperatures decrease with the decrease of laser energy input (the increase of laser scanning speed). Interestingly, the SLM-manufactured SMA exhibits ultrahigh tensile strength of 776 MPa and elongation of 7.2% under room-temperature tensile condition. In addition, stress-controlled cyclic tensile tests under 400 MPa indicate that the SLM-manufactured SMA has ultrahigh shape memory effect of 98.7% recovery ratio and 4.99% recoverable strain after ten times loading-unloading cycle. The ultrahigh mechanical and shape memory properties are associated to the combined effects of dispersedly distributed nano-sized Ti2Ni precipitates, ultrafine grains and profuse dislocations in the SLM-manufactured SMA. This work substantiates, for the first time, high enough energy input in SLM can be applied to manufacture ultrahigh-performance TiNi SMAs.

Wear Resistance and Morphological Characterization of High-power Laser Clad Coatings on Ti-6Al-4V Alloy

Ti-Si binary coatings were cladded on Ti-6Al-4V alloy surface for improvement morphological orientation, microstructure and surface properties. The coatings were developed at 2.1 kW power, laser scanning speed of 1.2, 1.6 and 2.0 m/min, spot diameter of 3 mm and 0.5 overlap ratio. An optical microscope was used to magnify and analyse the microstructural arrangement and a microhardness indenter used to measure microhardness at 100gf for 10 seconds. The indent spacing was maintained at 100 µm between adjacent indents. The phase content of the coatings was analyzed with XRD technique. The coating wear resistance was tested at 10N force loading for 7 minutes using a TRB tribometer and characterized using SEM. Clad coatings were observed to exhibit refinement in microstructure with an increase in laser scanning speed where transformation occurred from equiaxed grains with localized smaller grains to refined grain structure. The highest degree of refinement was observed at 2.0 m/min scanning speed. It was also found that the microhardness property was improved by 2.44, 2.60 and 2.64 times the microhardness of Ti-6Al-4Vat 342.3 HV0.1. It is understood that high microhardness values favor improved wear resistance behavior. XRD analysis on the coatings revealed presence of Ti5Si3, Ti, Si and TiSi2 phases where Ti and Si are in matrix capacity and Ti5Si3 and TiSi2 present as intermetallic phases. The reported improvement in microhardness was attributed to the presence of Ti5Si3 and TiSi2. The action of the laser scanning speed was found to influence the clad height where an increase in laser scanning speed resulted in a decrease in clad height in the order 685.9, 491.4 and 291.5 µm for 1.2 m/min, 1.6 m/min and 2.0 m/min respectively. Wear test indicated that the coatings displayed an improved wear resistance by evidence of little material removal exhibited, compared to the substrate material which was dilapidated by severe adhesive wear and further aggravated by plastic deformation.

Experimental and Taguchi-Based Grey Approach of Laser Metal Deposition Technique on Nickel-Based Superalloy

Thin sections of Inconel 718 sample was treated with laser-based metal deposition using a CW CO2 laser. The Taguchi-based grey relational approach was incorporated for determining the optimized process characteristics of the laser treatment. Laser scan speed was varied at a constant laser power in order to analyze the effect of cooling rate and the subsequent thermal gradient on the microstructure and other properties of the base alloy. The presence of γ′-(Ni3Al, Ni3Ti) and γ″-Ni3Nb precipitates in the interdendritic boundaries was evidenced in the deposition zone. The increase in laser scan speed to 600 m/min changed the microstructure from coarse to fine grains, and a further increase to maximum laser power of 1.75 kW showed the transformation to still finer dendritic structure. Even though the fine dendritic structure, it also resulted in delamination of bonding layers which could be deleterious. X-ray diffraction spectrum revealed the precipitation of γ-NiCr, γ′-Ni3Al and γ″-Ni3Nb in the γ-Ni matrix and there was no evidence for the transformation of γ″-Ni3Nb to δ-Ni3Nb. It indicated that the selected laser parameter had the least possibility of influence in the formation of intermetallics after treatment. The significant effect of grain refinement improved the hardness by 15–20%. The tensile test on Inconel 718 showed the Ni3Nb precipitate particles initiated the interfacial failure and was encountered with ductile mode of fracture.

Influence of laser scanning speed on nitrided Ti6Al4V surface

ABSTRACT The influence of laser scan speed during nitriding in the range 30–150 cm min−1 on the physical properties, microstructure and corrosion behaviour of Ti6Al4V was studied. The surface energy of nitrided Ti6Al4V remained almost constant up to the scan speed of 60 cm min−1 followed by an increase in the maximum value at 80 cm min−1. A gradual drop in the microhardness of the coating from the outermost surface was noticed for specimens nitrided up to 80 cm min−1; an abrupt decrease, however, was found at a scan speed ≥100 cm min−1. The laser nitriding produced dendritic microstructure; an exponential decay in the secondary dendrite arm spacing (SDAS) with the increase in laser scan speed was revealed. The SDAS produced was smaller at the interphase and centre of the coating, compared to that at outermost surface. The passivation behaviour of Ti6Al4V at lower potentials shifted to the smaller current side after laser nitriding.

Effect of laser scanning speed on a Ti-45Al-2Cr-5Nb alloy processed by selective laser melting: Microstructure, phase and mechanical properties

This work presents a comprehensive study on the laser scanning speed on the microstructure development, phase evolution and nanohardness of a TiAl alloy, Ti-45Al-2Cr-5Nb (at.%), processed by selective laser melting (SLM). The experimental results show that when increasing the laser scanning speed from 500 to 800 mm/s, the average grains size decreases from 7.11 μm to 5.43 μm, whereas the crystallographic texture showing a combination of (0001), (101¯1) and (112¯1) orientations basically remains unchanged. The SLM-processed TiAl alloy is dominated by high-angle (>15°) grain boundaries (HAGBs) and the contents of HAGBs decrease from 91.6% to 86.1% when the laser scanning speed varies from 500 to 800 mm/s. The α2 phase decreases while the γ and B2 phases increase with increasing the laser scanning speed. Moreover, the phase evolution mechanism in the SLM-processed TiAl alloy can be described as follows: (200) β transforms to (202¯0)α2 and (110) γ, and then the residual B2 and the incompletely transformed γ phase randomly distributed in the α2 phase matrix. The nanohardness of the SLM-process TiAl alloy increases from 7.90 ± 0.32 GPa to 9.49 ± 0.46 GPa with increasing laser scanning speed from 500 to 800 mm/s, which is much higher than those of traditionally manufactured counterparts, such as casting parts (4.98 ± 0.10 GPa) and TiB2 reinforced TiAl alloy fabricated by roll bonding (6.73 GPa). With the increase of laser scanning speed from 500 to 800 mm/s, compression properties of the SLM-process TiAl alloy increases from 829.41 ± 24.88 MPa to 1216.16 ± 36.48 MPa.

Characterization of heat affected zone liquation cracking in laser additive manufacturing of Inconel 718

The heat affected zone liquation cracking behavior was studied in laser additive manufactured Inconel 718. Liquation cracking was found initiating from the weak site near the fusion line in the pre-deposited layer, propagating along the interdendritic region with the further deposition proceeding layer by layer. Total cracking length calculation results showed that when controlling the heat input and height increment constant, liquation cracking susceptibility increased with the increase of laser scanning speed; and when controlling the laser scanning speed and height increment constant, liquation cracking susceptibility increased with the increase of heat input. The effect of grain boundary misorientation on susceptibility to liquation cracking was also investigated through electron backscatter diffraction (EBSD) measurement, and the results showed that liquation cracking tendency increased with the increase of grain boundary angle, which was considered to be attributed to the higher stability of liquation film at larger grain boundary during the last stage of solidification.

Microstructure and Mechanical Characterization of Laser Sintered Inconel-625 Superalloy

Direct metal laser sintering (DMLS) is an additive manufacturing technology that uses a high power laser to produce three dimensional parts by sintering metal powders spread on the substrate under protective inert gas environment. This paper focuses on direct metal laser sintering of Inconel-625 super alloy and its characterization. Inconel-625 material was sintered on steel substrate by varying the laser scan speed from 2.5 to 10mm/s in steps of 2.5, hatch spacing from 0.2 to 0.4mm in steps of 0.1, while laser power, hatch width and layer thickness were maintained constant at 240W, 5mm, 50μm respectively with laser beam diameter of 0.4mm. The build orientation during sintering was such that the axis of the cylindrical specimens was parallel to the build direction. Nitrogen atmosphere was maintained in the build chamber. The studies clearly reveal that with increase in laser scan speed and hatch spacing there was an increase in microhardness of the sintered parts while there was a decrease in dimensional accuracy, and density.

Influence of laser scanning speed on Cu-Zr-Al composite coatings on Mg alloys

To improve the surface properties of magnesium alloys, a study was conducted on Cu-Zr-Al composite coatings on AZ91HP magnesium alloy by laser cladding. The influence of laser scanning speed on the microstructures and properties of the coatings was discussed. The coatings consist of amorphous phase, Cu8Zr3, and Cu10Zr7. With the increase of laser scanning speed, the amorphous phase content of the coatings increases and reaches 60.56wt% with the laser scanning speed of 2.0 m/min. Because of the influence of laser scanning speed on the amorphous and crystal phases, the coatings show the maximum elastic modulus, hardness, and wear resistance at the laser scanning speed of 1.0 m/min. At the laser scanning speed of 2.0 m/min, the coatings have the best corrosion resistance.

Microstructures, mechanical properties and corrosion resistance of Hastelloy C22 coating produced by laser cladding

The Hastelloy C22 coatings H1 and H2 were prepared by laser cladding technique with laser scanning speeds of 6 and 12mm/s, respectively. Their microstructures, mechanical properties and corrosion resistance were investigated. The microstructures and phase compositions were studied by metallurgical microscope, scanning electron microscope and X-ray diffraction analysis. The hardness and scratch resistance were measured by micro-hardness and nanoindentation tests. The polarization curves and electrochemical impedance spectroscopy were tested by electrochemical workstation. Planar, cellular and dendritic solidifications were observed in the coating cross-sections. The coatings metallurgically well-bonded with the substrate are mainly composed of primary phase γ-nickel with solution of Fe, W, Cr and grain boundary precipitate of Mo6Ni6C. The hardness and corrosion resistance of steel substrate are significantly improved by laser cladding Hastelloy C22 coating. Coating H2 shows higher micro-hardness than that of H1 by 34% and it also exhibits better corrosion resistance. The results indicate that the increase of laser scanning speed improves the microstuctures, mechanical properties and corrosion resistance of Hastelloy C22 coating.

Ultra-short pulse laser deep drilling of C/SiC composites in air

Ultra-short pulse laser machining is an important finishing technology for high hardness materials. In this study, it demonstrated that the ultra-short pulse laser can be used to drill the film cooling holes and square holes in aero-engine turbine blades made of C/SiC composites. Both the edges and bottoms of the drilling holes are covered with small particles. The following factors have a great effect on drilling holes according to this work: (1) circular holes can be processed only at a relative small helical lines spacing. (2) With the increase of laser scanning speed, the depth of holes reduces while the diameter rarely changes. (3) Through the holes of high aspect ratio can be obtained via high processing power.