A mathematical model to predict the thermal history and microstructure developed in laser surface alloying

Purpose: of this paper was to examine the corrosion resistance of laser surface alloyed (LSA) stainless steels using electrochemical methods in 1M NaCl solution and 1M H2SO4 solution. The LSA conditions and alloying powder placement strategies on the material's corrosion resistance were evaluated. Design/methodology/approach: In the present work the sintered stainless steels of different microstructures (austenitic, ferritic and duplex) where laser surface alloyed (LSA) with elemental alloying powders (Cr, FeCr, Ni, FeNi) and hard powders (SiC, Si3N4) to obtain a complex steel microstructure of improved properties. Findings: The corrosion resistance of LSA stainless steels is related to process parameters, powder placing strategy, that determines dilution rate of alloying powders and resulting steel microstructure. The duplex stainless steel microstructure formed on the surface layer of austenitic stainless steel during LSA with Cr and FeCr reveal high corrosion resistance in 1M NaCl solution. The beneficial effect on corrosion resistance was also revealed for LSA with Si3N4 for studied steels in both NaCl and H2SO4 solutions. Ferritic stainless steel alloyed with Ni, FeNi result in a complex microstructure, composed of austenite, ferrite, martensite depending on the powder dilution rate, also can improve the corrosion resistance of the LSA layer. Research limitations/implications: The LSA process can be applied for single phase stainless steels as an easy method to improve surface properties, elimination of porosity and densification and corrosion resistance enhancement regarding as sintered material. Practical implications: The LSA of single phase austenitic stainless steel in order to form a duplex microstructure on the surface layers result in reasonably improved corrosion performance. Originality/value: The original LSA process of stainless steels (austenitic, ferritic and duplex) was studied regarding corrosion resistance of the alloyed layer in chloride and sulphate solutions.

Laser surface alloying of AISI 304-stainless steel with molybdenum for improvement in pitting and erosion–corrosion resistance

A dimensional analysis of laser surface alloying (LSA) using measurable experimental variables and known thermophysical properties has been carried out to identify useful dimensionless parameters influencing LSA. Measured solute contents from a two-level factorial experiment alloying nickel into AISI 1020 steel substrates are plotted against these parameters and found to vary hyperbolically. Similar trends are shown to be contained in published data alloying chromium into 1020 steel. The two parameters make good physical sense, point to mechanisms in LSA, and may be used for process control. One parameter is the laser surface alloying parameter (LASAP), where LASAP = P/pud2, and P is incident laser power (W), p is surface gas pressure (N/m2), u is traverse speed (m/s), and d is beam diameter (m). The other is the laser processing parameter (LAPP), where LAPP = Pd/(pau2d2) and p, d, u are as above, whilep is the substrate density (kg/m3) and a is the substrate thermal diffusivity (m /s).

Laser surface remelting and alloying of sintered stainless steel type 410L with FeNi and Ni have been studied for improvement of corrosion resistance and hardness increase. The influences of high power diode laser (HPDL) processing conditions, laser power in range 0.7-2.1 kW on the microstructure and properties of alloyed surface layer have been evaluated. The FeNi alloyed layer shows microstructure composed of austenite and martensite formed, due to high cooling rate in laser remelting process, with average Ni content in range of 39 to 8% depending on laser processing conditions. The Ni alloyed layer was composed of austenitic microstructure with Ni content from 65% to 33%. The improvement in microhardness was achieved by laser surface alloying and remelting. Excellent corrosion properties were observed for such remelted and alloyed layers in salt spray test.

The paper presents results of the effect of laser surface remelting and alloying by carbides powders of NbC, TaC, TiC, VC and WC on the structure and thermal fatigue resistance of the surface layer of hot work tool steels X40CrMoV5-1 and 32CrMoV12-28. The laser surface alloying and remelting treatments was performed using a high power diode laser (HPDL ROFIN SINAR DL 020). In order to investigate the effect of applied laser treatments and used alloying powders on the microstructure and thermal fatigue resistance of processed surface layer of hot work tool steels, the microstructure evaluation by light microscopy, hardness test, and dedicated thermal fatigue resistance test were performed. The best results regarding fatigue cracks inhibition was obtained when the surface of hot work tool steels was alloyed with TiC and VC carbides at the laser beam power of 2.0 and 2.3 kW. The grain refinement effect of laser remelting has a lower impact on the thermal crack inhibition, than a strong strengthening effect of matrix saturation in alloying elements and precipitation of fine carbides in the steel matrix.

Development of wear resistant composite surface on mild steel by laser surface alloying with silicon and reactive melting

In this study, two techniques such as laser surface melting (LSM) and laser surface alloying (LSA) were performed to protect the surface layers of nodular cast iron as it is used to manufacture different machine parts like cams, beds, camshafts, crankshafts, cylinders and engine blocks. The main objective of this research work is to examine the effects of LSM and LSA processes on phases, microstructure, hardness, wear resistance and surface roughness. The outcomes of both LSM and LSA specimens show a homogeneous structure, effective bonding of alloy powders with the base metal and crack-free surfaces. The hardness was improved 4 times (LSM) and 2.62 times (LSA) when compared with the base material. The tribological test shows improved wear resistance of LSM (8.82 × 10−7 kN) and LSA (1.32 × 10−6 kN) samples compared to the base material (4.36 × 10−6 kN). The examined wear tracks indicate that mild abrasion, adhesion and delamination were the major wear mechanisms. The reason for the enhancement of wear resistance is the refinement of microstructure, the solid solution strengthening effect and good bonding between alloy powders and base material. The LSM technique is a potential method to improve the tribological properties of industrial materials.

In the present study, an attempt has been made to enhance the corrosion resistance of a Mg alloy (MEZ) by laser surface alloying with Al + Mn. Laser surface alloying has been carried out with a 10 kW continuous wave CO 2 laser by melting and simultaneous feeding of a powder mixture of Al and Mn in the ratio of 3 : 1 and 1 : 3, respectively. Following laser irradiation, the alloyed zone has been characterized by a detailed microstructural observation and phase analysis. Moreover, the properties of the surface alloyed layer like microhardness and corrosion have been evaluated in detail. The surface modified layer predominantly consists of dendrites of Al + Mn and Al + Mg. The microhardness of the alloyed zone has been significantly enhanced to as high as 250-350 VHN as compared to 35 VHN of the substrate region. The corrosion rate in a 3.56 wt.% NaCl solution has significantly reduced to 250 mpy for laser surface alloyed specimen as compared to 1520 mpy of the MEZ substrate. The enhanced corrosion resistanc...

In the present study, laser surface alloying of aluminum with magnesium, manganese, titanium and zinc, respectively, was carried out to improve acid corrosion resistance. Laser surface alloying was conducted using 1600 and 1800 W power source using CO2 laser. Acid corrosion resistance was tested by dipping the samples in a solution of 2.5% H2SO4 for 200 h. The weight loss due to acid corrosion was reduced by 55% for AlTi, 41% for AlMg alloy, 36% for AlZn and 22% for AlMn alloy. Laser surface alloyed samples offered greater corrosion resistance than the aluminum substrate. It was observed that localized pitting corrosion was the major factor to damage the surface when exposed for a long time. The hardness after laser surface alloying was increased by a factor of 8.7, 3.4, 2.7 and 2 by alloying with Mn, Mg, Ti and Zn, respectively. After corrosion test, hardness was reduced by 51% for AlTi sample, 40% for AlMg sample, 41.4% for AlMn sample and 33% for AlZn sample.

The unique characteristics of the laser beam such as directionality, monochromaticity, and brightness make it a very important tool in the surface treatment engineering. The concentrated heat in the laser beam can be precisely directed toward the processed region on the surface. The laser beam power, beam size, and scanning velocity are easily controlled during the different processing methods. Laser surface modifications of metallic materials, such as laser surface melting, laser surface alloying, and laser cladding are some of the most important methods to improve the mechanical properties of the processed layer on the surface. A pulsed Nd-YAG laser surface melted specimens of low carbon steel with a maximum power of 90W at different processing parameters. The rapid melt and solidification of the treated layer produced a refinement in the microstructure. The original microstructure of this steel (Ferrite + Pearlite) has been transformed to new phases of martensitic and bainitic structures. The melted layer consists of the melted pool, the heat affected zone, and the substrate. The maximum hardness of the laser melted layer is more than 400 HV. The effect of different lasers such as high power CW CO2 laser on the mechanical properties and corrosion resistance of steel alloys will be carried out in future studies. Keywords: Nd-Yag Laser, Laser surface treatment, Microstructure and hardness of AISI1012 steel

Development of graded composition and microstructure on Inconel 718 by laser surface alloying with Si, Al and ZrB2 for improvement in high temperature oxidation resistance

Laser surface alloying of copper with chromium

Laser surface alloying of a marine propeller bronze using aluminium powder: Part I: Microstructural analysis and cavitation erosion study

Ceramics are one of the best engineering materials for coating gas turbine blades. In this study, the Metco204NS ceramic coating (Zr2O + 8%Y2O3) was applied by the laser surface alloying (LSA) method on IN713 LC nickel-based superalloy. To influence the heat input on the structure of the ceramic coating and its substrate, and as well as the rejuvenated zone (RZ), different variables were used in LSA. The results showed that with an increase in heat input by the laser, the sensitivity to liquation cracks in the heat affected zone and solidification cracks in the RZ decreases. The most important reason for this was the increase in backfilling by the molten metal due to its high fluidity. However, with increasing heat input, the hardness increased due to the reduction of the distance between the dendrites. Solidification rate (R) and temperature gradient (G) were identified as the most important microstructure controlling factors in the RZ. So, with increasing the heat input and thus decreasing G and R, the tendency of the structure to change from cellular to columnar and then equiaxed increased. The uniform and homogeneous coating of Metco 204NS significantly increased the wear resistance of IN713 LC superalloy. The higher hardness and wear resistance of melted Metco 204NS coating material relative to the RZ and the base metal was due to the presence of very hard Zr2O and Y2O3 particles in Metco 204NS and the reduction of grain size.

A novel proposal to manipulate the properties of titanium parts by laser surface alloying