ON THE COMPOSITION UNIFORMITY AND SHAPE COEFFICIENT OF MOLTEN POOL BY LASER ALLOYING

The effect of the laser processing parameters on the composition uniformity and shape coefficient of fusion zone with laser surface alloyed Cr plated on medium carbon low alloy steel has been studied.It was found that the composition uniformity depends on the shape coefficient of fusion zone,and the later is a function of both power density and interaction time.If the power density is fixed to a certain value,the shape coefficient is directly,propor- tional to the interaction time.A completely,uniform molten pool can be obtained,when the shape coefficient is between 1.6 and 3.0.

Cavitation erosion behavior of WC coatings on CrNiMo stainless steel by laser alloying

The WC powder was precoated on the surface of CrNiMo stainless steel and then made into an alloying layer by using the laser alloying technique. Phases in the layers were investigated by X-ray diffraction （XRD） analysis and surface morphologies after cavitation erosion were observed with the help of scanning electron microscopy （SEM）. The cavitation erosion behavior of the CrNiMo stainless steel and WC laser alloying layer in distilled water was tested with the help of ultrasonic vibration cavitation erosion equipment. The results showed that the thickness of the laser alloying layer was about 0.13 mm. The layer had a dense microstructure, metallurgically bonded to the substrate, and no crack had been found. The cavitation erosion mass loss rate of the laser alloying layer was only 2/5 that of the CrNiMo stainless steel. The layer had better cavitation resistance properties because of its metallurgical combination and the strengthening effects of the precipitate phases.

Fabrication of wear-resistant layers with lamellar eutectic structure by laser surface alloying using the in situ reaction between Cr and B_4C

To improve the wear resistance of Cr5 steel, wear-resistant layers with lamellar eutectic microstructure were fabricated by laser surface alloying（LSA）, which is dependent on the in situ reaction between Cr and B_4C. Our results indicated that the hypoeutectic structures of the LSA layers were divided into interdendritic eutectic structures and dendrites. The area fraction of the eutectic structures increased with increasing laser scanning speed, which improved the hardness and wear resistance of the LSA layers. The average hardness of the LSA layer prepared at a scanning speed of 8 mm/s was HV_（0.2） 883.9, which was 1.8 times greater than that of the traditional quenched layer（approximately HV 480）. After sliding for 659.4 m, the specimen prepared at a scanning speed of 8 mm/s exhibited a volume loss of 0.0323 mm^3, which was only 29.5% of the volume loss of the traditional quenched specimen.

EVOLUTION OF MICROSTRUCTURE OF LASER SURFACE ALLOYING OF γ TiAi ALLOY WITH NITROGEN

Laser surface alloying of γ TiAl alloy with nitrogen was studied under the constant protective nitrogen current (20l /min). The experimental results shown that the surface multi layers formed with experimental parameters could be up to 600μm depth; it consists of TiN,Ti 2AlN,α 2 and γ phases, without AlN, and the irregular coarse continuous “flow” line,dendrite,needle and granular nitrides disperse on the fine dendrite casting α 2 and γ phases substrate. The microstructure and compositions in the nitiding layer were determined and analyzed by SEM and EPMA and the mechanism for the formation of microstructure in the nitriding layer was also discussed.

Optimizing Domain Distribution of Grain Oriented Silicon Steel by Using Antimony as the Laser Surface Alloying Element

For reducing the core loss of grain oriented silicon steel and improving its aging property, a new method, the LLSA by using Sb as the laser surface alloying element, was investigated, and at proper technique conditions rather good result was obtained.

Laser Alloyed Coatings of TiB_2/Graphite on 9Cr18 Stainless Steel Surface

Modified coatings including carbide of iron, nickel, chromium, silicon, and titanium are obtained on 9Cr18 stainless steel surface by laser alloying. The processing method, the microstructure, the interface, the tribological properties, and the forming mechanisms of the coatings are analyzed. The results show that the microstructure of the alloyed coatings is mainly irregular FeC crystals. Carbides of chromium and iron are around the FeC crystals. Small granular TiC disperses in the alloyed coatings. The microhardness of the alloyed coatings is greatly improved because of the occurrence of carbide with high hardness. At the same time, the wear resistance of the alloyed coatings are higher than that of 9Cr18 stainless steel.

Influence of niobium and molybdenum addition on microstructure and wear behavior of laser-borided layers produced on Nimonic 80A-alloy

Laser alloying was used for production of thick layers on surface of Nimonic 80A-alloy.For laser surface modification,three types of pre-coated pastes were applied:with amorphous boron,with amorphous boron and molybdenum as well as with amorphous boron and niobium.The microstructure,hardness and wear resistance of produced layers were studied in details.The presence of different types of borides in re-melted zone depended on the paste composition and caused an increase in hardness up to about HV 1000.The wear resistance was evaluated by calculation of mass wear intensity factor Imw and relative mass loss of specimen and counter-specimen.The wear behavior of the tested frictional pairs was determined by 3D interference microscopy,scanning electron microscopy equipped with EDS microanalyzer.The significant increase in abrasive wear resistance was observed in comparison to untreated Nimonic 80A-alloy.The lowest mass loss intensity factor was characteristic of laser-alloyed Nimonic 80A-alloy with boron and niobium(Imw=1.234 mg/(cm2?h)).Laser alloyed-layers indicated abrasive wear mechanism with clearly visible grooves.Laser alloying with boron and niobium resulted in the additional oxidative wear mechanism.In this case,EDS patterns revealed presence of oxygen on the worn surface of specimen.

Optimization of tribological parameters over WC-12%Co laser alloyedpearlitic ductile iron using Taguchi based Grey relational analysis

Pearlitic ductile irons(PDIs)are used in transportation and nuclear energy industries.In heavy loading situation,the service life of PDI is affected by numerous tribo aspects.In this study,surface of the PDI is alloyed with WC-12%Co powder using a high power fibre laser.The wear properties of the base material and laser alloying samples were investigated by tribometer with various parameters,i.e.,temperature,load and sliding speed.Based on experimental test,the load has maximum percentage of contribution and followed by sliding speed and working temperature.The optimized tribological parameters by Grey relational analysis(GRA)were established and those values are closely matched with predicted values.Besides,base material and laser alloying surfaces were examined through Vickers hardness machine,scanning electron microscopy(SEM)and roughness tester.The laser altered specimen shows no defects and improves the wear properties than substrates.The identified optimal tribological parameters are load of 30 N,speed of 0.5 m/s and working temperature of 300℃,and load of 30 N,speed of 0.5 m/s and working temperature of 200℃ for base metal and laser alloying samples,respectively.

OBSERVATION ON MICROSTRUCTURE OF LASER MELTED TRANSITION ZONE

The surface alloying specimen was made from the steel 45 substrate overcoating by oxygen-acetylene flame spraying Fe-Cr-Ni alloy powder and laser remelting.The chemical heterogeneity was clearly observed on the transition zone between the laser melted zone and heat-affected zone by means of EPMA,AES and SEM.This heterogeneity is rather serious during high temperature tempering,so the decarburization on the transition zone side and the recarburization on the melted zone side were found.

Study on Addition of Yttrium to Heat-Resistant Materials by Laser Surface Melting

Addition of rare earth(RE)such as Y in the surface layer of gray cast iron or Ni-based superalloy by laser sutface melting was carried out using a 2 k W CO_2 laser.For delivering the element Y to the metal surface dur- ing laser irradiation,several methods were employed.It is found that Y-containing surface modified layer can he controllably obtained on substrates,a gray cast iron can be laser surface-modified with Cr+Al-Y powder re- sulting in a thin layer of Fe-Cr-Al-Y alloy such as 30Fe40Cr27Al3Y.

ELECTRON MICROANALYSIS FOR LASER MELTED ZONE IN 45 STEEL WITH Fe-Ni-Cr COATING

The Fe-Ni-Cr coating laver has been alloyed with 45 steel base metal by transverse.flow type CO_2 gas laser of maximum output 5kW.The characteristics of the melted zone and the es- sence of the“bright band”has been investigated using the electron microscopy.The results show that the“bright band”belongs to the melted zone and is a vertical section of the plane crystal,The width of the“bright band”equals the height of the plane crystal,which decreases with the increase of laser beam scanning rate and the decrease of laser power.This has been explained in terms of constitutional supercooling G/R.

Influence of CeO_2 on Corrosion Resistance of Laser Alloyed M_（80）S_（20） Alloy Layer

On the basis of previous work,the influence of CeO_2 on the corrosion resistance of laser-alloyed M_(80)S_(20),where M signified a metallic content,predominantly iron,and S represents a metalloid content specifically boron,silicon,and carbon,was further studied by comparative electrochemical test using optical microscope,scanning electron microscope,potentiostat and a X-Y recorder in this paper.The results shown that the addition of CeO_2 can improve the corrosion resistance of laser-alloyed M80S20 alloy layer significantly.

The Process of a Laser-Supported Combustion Wave Induced by Millisecond Pulsed Laser on Aluminum Alloy

We study the process of a laser-supported combustion wave （LSCW） when an aluminum alloy is irradiated by a millisecond pulse laser based on the method of laser shadowgraphy. Under the condition of different laser parameters, the obtained results include the velocity, ignition threshold of LSCW and the variation law. The speed of LSCW increases with the laser energy under the same irradiation laser pulse width, and the speed of LSCW reduces with the increase of the laser pulse width under the same irradiation laser energy. Moreover, the ignition time of LSCW becomes shorter by increasing the laser number of the pulse and is not effected by changing the frequencies, when keeping the laser pulse width and energy unchanged. The results of the study can be applied in the laser propulsion technology and metal surface laser heat treatment, etc.

Laser repairing surface crack of Ni-based superalloy components

Surface crack of components of the cast nickel base superalloy was repaired with twin laser beams under proper technological conditions. One laser beam was used to melt the substrate material of crack, and the other to fill in powder material to the crack region. The experimental results show that the surface crack with the width of 0.1 ～ 0.3?mm could be repaired under the laser power of 3?kW and the scanning speed of 6 ～ 8?mm/s. The repaired deepness of crack region is below 6.5?mm. The microstructure of repaired region is the cellular crystal, columnar crystal dendrite crystal from the transition region to the top filled layer. The phases in repaired region mainly consisted of supersaturated α Co with plenty of Ni, some Cr and Al, Cr 23 C 6, Co 2B, Co Ni Mo, Ni 4B 3, TiSi and VSi. The hardness of filled layer in repaired region ranged from HV 0.2 450 to HV 0.2 500, and the hardness decreases gradually from the filled layer to joined zone.

Fracture Behaviour of Laser Clad Fe-and Ni-base Alloy Coatings on a Cast Iron under SEMI Loading

Laser cladding technique has been applied to renovate some partially-damaged (or worn) components with Fe, Ni, Co-base alloys, hence to improve their hardness values and wear resistance successfully in previous reports. But for some punching or shearing cast iron dies damaged or worn in automobile manufacture, the renovated surfaces also bear some impact loading. Therefore, a small-energy and multi-impact (SEMI) test was designed to investigate the fracture behaviour of renovated cast iron dies achieved by laser cladding of Fe and Ni-base alloys under SEMI loading to meet above requirement. observations show that the fracture took place in the substrate near to the substrate/coating interface rather than at the interface. The tempering temperature has a great influence on the cycles to fracture of laser-clad samples under SEMl loading, i.e. the low tempering temperature of 300℃ gives a maximum cycle to fracture, while a higher tempering temperature of 400℃ has a minimum. Furthermore, the fracture mechanism has also been discussed in present study

Corrosion Resistance of AZ91 Magnesium Alloy after Laser Remelting Treatment

The main objective of the study was the modification of the surface layer of magnesium alloy by the COlaser. The studied material was the commercial AZ91 magnesium alloy. The effectiveness of the alternations caused by the remelting process was verified on the basis of microscopic observation and corrosion investigations, i e, recording of potentiodynamic polarization curves, electrochemical noise measurements and hydrogen evolution rate measurements. For the adopted range of the treatment parameters, favourable changes were observed in the surface layer such as the refinement of structure and more uniform arrangement of individual phases. As a consequence of those favourable structural changes the improvement of the corrosion resistance of the alloy was achieved in comparison to its non-remelted equivalent. For the treated material corrosion rates expressed as corrosion current densities were at least three times lower than the appropriate values for the untreated alloy comparing them for the same period of samples immersion in the test solution. The obtained results have confirmed the effectiveness of the applied surface treatment resulting in favourable changes in the structure and corrosion properties of the AZ91 magnesium alloy.

STUDY OF THE MECHANISM TO IMPROVE PERFORMANCE OF CARBIDE BLADE BY LASER

The expermental research on the change of chemical composition and structure of car- bide blade surface treated by laser is carried out, and the relation between their structure and per- formance is studied. The result shows that the element Co exists as a simple substance phase in prim- itive sintering structure. while in new melt-sintering structure it forms a fine alloy phase with origi- nal carbide, and this is the main factor which improves the performance of carbide blade treated by laser.

Enhancement of mechanical and tribological performance of Ti-6Al-4V alloy by laser surface alloying with Inconel 625 and SiC precursor materials

This study focused on producing metal matrix composite(MMC)coatings on Ti–6Al–4V alloy through laser surface alloying using a novel combination of Inconel 625 and SiC precursor materials.Various ratios of alloying powders were examined to evaluate surface properties such as microhardness,wear resistance,and friction coefficient,along with analyzing the phase composition and microstructure of the coatings.The in situ synthesized MMC coatings exhibited the presence ofα-Ti,NiTi,NiTi_(2),and TiC phases.Additionally,Ti_(5)Si_(3)andα-Ti/Ti_(5)Si_(3)eutectic structures were observed when the SiC content exceeded 20%.In comparison to the titanium substrate,the MMC coating significantly enhanced microhardness by over threefold and reduced wear by 95%.However,it was crucial to carefully select the appropriate combination of alloying powders to avoid a substantial decrease in friction performance and excessive formation of cracks.Through a comparative analysis of experimental results,the optimal precursor material composition was identified as 85%Inconel 625 and 15%SiC.This study demonstrated the effective utilization of Inconel 625 and SiC alloying materials to enhance the surface properties of titanium alloys,thereby expanding their application in challenging environments.

Influence of yttrium on laser surface alloying organization of 40Cr steel

In order to improve the performance of the metal rollers, Mo＋Y2O3 alloy powders were used to coat uniformly on the surface of 40Cr steel roller substrates for the laser surface alloying treatment by a CO2 laser, The results showed that many good consequences were ob- tained after adding the rare earth oxide Y2O3. The crystal grains of the alloy layer were significantly refined. The boundary of crystal grains was strengthened. The unifomaity and density of the microstructure were increased. The hardness and wearing resistance of the alloy layer were considerably improved. The valence electron structure analysis of the alloy layer was made by the empirical electron theory of solids and molecules （EET）. The calculated results demonstrated that Y should be mixed in the first stage and Fe should be in the eighteenth hybrid bands. The analyzed outcomes illustrated that the electron theory of the solid solution shows the strengthening effect on the alloying layer, which has enhanced bond and confirrned the experimental results.

Laser Surface Alloying of Low Carbon Steel Using High-entropy Alloy Precursors

The Al0. 5CoCrCuFeNi high-entropy alloy powders with simple face-centered-cubic （FCC） solid solution structure were introduced into the surface layer of a low carbon steel during laser surface alloying. A high performance surface layer with extremely fine martensite as the dominant phase was obtained, resulting in a great improvement in microhardness, wear resistance, and corrosion resistance. The great enhancement of microhardness and wear resistance of the laser alloyed layer is mainly due to the formation of extremely fine martensite hard phase, the solid solution strengthening of the alloying e!.ements in supersaturated a-Fe solid solution, and the existence of size effect and strain effect under rapid solidification. The enhancement of corrosion resistance is due to the alloying of Al, Co, Ni, Cr and Cu in the laser alloyed layer.