Atomic diffusion in laser surface modified AISI H13 steel

This paper presents a laser surface modification process of AISI H13 steel using 0.09 and 0.4 mm of laser spot sizes with an aim to increase surface hardness and investigate elements diffusion in laser modified surface. A Rofin DC-015 diffusion-cooled CO2 slab laser was used to process AISI H13 steel samples. Samples of 10 mm diameter were sectioned to 100 mm length in order to process a predefined circumferential area. The parameters selected for examination were laser peak power, pulse repetition frequency (PRF), and overlap percentage. The hardness properties were tested at 981 mN force. Metallographic study and energy dispersive X-ray spectroscopy (EDXS) were performed to observe presence of elements and their distribution in the sample surface. Maximum hardness achieved in the modified surface was 1017 HV0.1. Change of elements composition in the modified layer region was detected in the laser modified samples. Diffusion possibly occurred for C, Cr, Cu, Ni, and S elements. The potential found for increase in surface hardness represents an important method to sustain tooling life. The EDXS findings signify understanding of processing parameters effect on the modified surface composition

Laser Surface Modification of H13 Die Steel using Different Laser Spot Sizes

This paper presents a laser surface modification process of AISI H13 tool steel using three sizes of laser spot with an aim to achieve reduced grain size and surface roughness. A Rofin DC'015 diffusion'cooled CO2 slab laser was used to process AISI H13 tool steel samples. Samples of 10 mm diameter were sectioned to 100 mm length in order to process a predefined circumferential area. The parameters selected for examination were laser peak power, overlap percentage and pulse repetition frequency (PRF). Metallographic study and image analysis were done to measure the grain size and the modified surface roughness was measured using two'dimensional surface profilometer. From metallographic study, the smallest grain sizes measured by laser modified surface were between 0.51 3m and 2.54 3m. The minimum surface roughness, Ra, recorded was 3.0 3m. This surface roughness of the modified die steel is similar to the surface quality of cast products. The grain size correlation with hardness followed the findings correlate with Hall'Petch relationship. The potential found for increase in surface hardness represents an important method to sustain tooling life

Optimization of Pulsed Nd:YAG Laser Melting of Gray Cast Iron At Different Spot Sizes for Enhanced Surface Properties

This paper presents a laser surface modification process of gray cast iron using different laser spot size with an aims to eliminate graphite phase and achieve minimum surface roughness and maximum depth of molten zone and microhardness properties. The laser processing was conducted using JK300HPS Nd:YAG twin lamp laser source pulse TEM 00 mode, 50 W average power, 1064 nm wavelength and different laser spot sizes of 1.0 mm, 1.2 mm, 1.4 mm and 1.7 mm. Three controlled parameter were peak power (Pp), pulse repetition frequency (PRF) and traverse speed (v). Increasing spot size the parameter setting where peak power is increased and pulse repetition frequency and traverse speed is decreased. The modified surface of laser surface melting was characterized for metallographic study, surface roughness and hardness. Metallographic study and surface morphology were conducted using optical microscope while hardness properties were measured using Vickers scale. Surface roughness was measured using a 2D stylus profilometer. From metallographic study, the graphite phase was totally eliminated from the molten zone and formed white zone. This phenomenon affected hardness properties of the modified surface where maximum hardness of 955.8 HV0.1 achieved. Optimization of laser surface modification was conducted for minimum surface roughness and maximum depth of modified layer and hardness properties. From the optimization, the higher desirability is 0.902. The highest depth of molten zone obtain from spot size 1.4 mm at 132 µm and the highest hardness is 989 HV0.1 at laser’s spot size 1.0 mm. The surface roughness increased when the spot size increased from 3.10 µm to 7.31 µm. These finding indicate potential application of enhanced gray cast iron in high wear resistance automotive components such as cylinder liner and break disc

Thermal fatigue properties of laser treated steels

This paper presents the thermal fatigue resistance of laser treated steels. The C40 and AISI H13 steels were machined into a geometry which allowed thermal gradients on the inner and outer surface during testing. A CO2 laser system was used with a focused spot size of 0.09 mm on the sample surface. The laser peak power and pulse repetition frequency (PRF) range were set to 760 and 1515 W, and 2900 to 3500 Hz respectively. The thermal fatigue machine used consists of Nabertherm model cylindrical high temperature furnace with digital control panel, controlled temperature quenching system, and pneumatics control sample movement mechanism. The thermal fatigue test involved immersion of samples into molten aluminium, and quenched in ionised water emulsion at 17°C temperature. The quenching system equipped with thermocouple to control the water temperature. Testing was done at a total of 1,750 number of cycles. Internal surface cooling was controlled by water inlet and outlet tubes. Samples were cleaned using NaOH solution after thermal fatigue testing to remove oxides on the surface. The solution temperature and magnetic stirrer speed were set to 100°C and 4.5 rpm respectively. Samples were characterised using scanning electron microscope (SEM), energy discharge x-ray spectroscopy (EDXS) and 2D stylus profilometer. Presence of different phases on the sample surface were analysed from back-scattered detector micrographs. Heat checks were observed on laser glazed surface at several regions. Carbides and oxides elements were detected on the sample surface after the thermal fatigue test. The relationship between surface roughness of laser treated surface and thermal fatigue behaviour was investigated

Laser Micro-Processing Of Amorphous And Partially Crystalline cu45Zr48Al7 Alloy

This paper presents a microstructural study of laser micro-processed high-purity Cu45Zr48Al7 alloys prepared by arc melting and Cu-mould casting. Microprocessing of the Cu45Zr48Al7 alloy was performed using a Rofin DC-015 diffusion-cooled CO2 slab laser system with 10.6-µm wavelength. The laser was defocused to a spot size of 0.2 mm on the sample surface. The laser parameters were set to give 300- and 350-Wpeak power, 30% duty cycle and a 3000-Hz laser pulse repetition frequency (PRF). About 100-micrometer-wide channels were scribed on the surfaces of disk-shaped amorphous and partially crystalline samples at traverse speeds of 500 and 5000 mm/min. These channels were analysed using scanning electron microscopy (SEM) and 2D stylus profilometry. The metallographic study and profile of these processed regions are discussed in terms of the applied laser processing parameters. The SEM micrographs showed that striation marks developed at the edge and inside these regions as a result of the laser processing. The results from this work showed that microscale features can be produced on the surface of amorphous Cu–Zr–Al alloys by CO2 laser processing

Laser cladding process to enhanced surface properties of hot press forming die: A review

Laser cladding is one of the advance processes in laser surface treatments. The process involved a laser beam to combines another material that has different metallurgical properties on a substrate, whereby a very thin layer of the substrate has to be melted for it to achieve metallurgical bonding with minimal dilution of added material and substrate. The resulted properties were characterized by surface topography, subsurface microstructure, hardness, and residual stresses. The objective of this paper is to review the factors that affected of cladding process to get the best cladding, suitable to enhance hot press forming die surface and subsurface. The parameter control, metallurgical bonding between coating and substrate, and effect of powder size were discussed

Optimization of laser melting parameter to enhanced surface properties in hot press forming die

This paper presents laser melting process with various parameter to enhanced surface properties of AISI H13 tool steel. The design of experiment (DOE) optimisation was conducted to obtain significant model using regression analysis. DOE were analysed using response surface method (RSM) with Box-Behnken design approach. Design Expert 7 software was used to design parameter of laser melting process. The laser melting processes was conducted using Nd:YAG laser system with pulsed mode at a constant average power of 100 W, overlapping rate of 30 to 50%, peak power of 1700 to 2500 W and pulse repetition frequency (PRF) of 50 to 70 Hz respectively. The responses were characterised for sub-surface hardness, melt depth and surface roughness. The results show that optimum parameter of 2500 W peak power, 60 Hz PRF and 30% overlapping rate produced highest surface hardness of 793.7 HV0.1 with 0.21 mm melted depth and 3.89 µm surface roughness from experimental data. This finding was important to enhance properties of AISI H13 tool steel for hot press forming die using laser process

Surface modification of HVOF thermal sprayed WC–CoCr coatings by laser treatment

In this work the affects of laser characteristics on microstructure and microhardness of high velocity oxygen fuel sprayed (HVOF) WC–CoCr coatings were investigated. The coating was deposited with a Sulzer Metco WokaJet™-400 kerosene fuel and the laser surface treatments were applied using CO2 laser with 10.6 μm wavelength. Large variations in surface properties were produced from variation in the laser processing parameters. In total, four levels of peak power (100, 200, 300 and 350 W), four levels of spot diameter (0.2, 0.4, 0.6 and 1 mm) and three levels of pulse repetition frequency (PRF) were investigated. An initial set of tests were followed by a more detailed 33 factorial design of experiments. Pulse repetition frequency and duty cycle were set in order to maintain the same overlap in the x and y directions for the raster scanned sample spot impact dimensions. Overlaps of 30% were used in the initial tests and 10% in the more detailed trials. The results have shown that care must be taken to keep the irradiance at a relatively low level compared to uncoated surfaces. High irradiance can in this case result in rough and porous surfaces. Lower levels of irradiance are shown to provide more uniform microstructures, reduced porosity and increased microhardness

Mechanical characterisation of water-jet shot peened H13 tool steel surface

A wear-resistant surface is achievable via the surface treatment of various sources such as laser, water-jet, ion beam, and plasma. This paper investigates the parameters of water-jet shot-peened H13 tool steel for minimum surface roughness and maximum hardness properties. Water jet processing parameters are significant in determining the surface roughness as well as hardness properties. Water-jet shot-peened (WJSP) was used in this experiment to improve the surface properties of H13 tool steel. The parameters are pressure and feed rate of 172 MPa to 310 MPa and 2600 mm/min to 10000 mm/min. The shot-peened samples were characterised for surface topography, surface roughness, and hardness properties. A laser confocal microscope was used to determine the dimension of the modified surface from shot peening and average surface roughness. Hardness properties were measured using the Vickers scale. From topography analysis, the surface roughness reading on the shot-peened surface was measured as much as 6.88 µm to 14.06 µm. Minimum surface roughness measured was 6.88 µm on sample processed at pressure and feed rate 172 MPa and 2600 mm/min. The hardness properties of the shot-peened subsurface were between 196 HV and 227 HV. The resulted hardness properties were due to plastic deformation from abrasive particle bombardment during shot peening. The findings are important to designing enhanced surface properties for mould and die applications

Effects of Thermal Fatigue on Laser Modified H13 Die Steel

In order to improve the wear properties of H13 die steel, the thermal fatigue properties of AISI H13 tool steel were investigated at a varied number of cycles for enhancing surface hardness. A CO2 laser system was used with a 0.09mm focused spot size on the sample surface. The peak power of 1137kW and pulse repetition frequency (PRF) of 2300Hz were the parameters controlled. The Nabertherm model of a thermal fatigue machine used consisted of the cylindrical high temperature furnace with digital control panel, controlled temperature quenching system and pneumatics control sample movement mechanism. The samples were immersed in molten aluminum and quenched in ionized water emulsion at 17oC temperature within a specific time per cycle. The quenching system was equipped with a thermocouple to control the water temperature. The testing was done on1,750 and 3,500 cycles. The treated samples was characterized for metallographic study and hardness. The metallographic study was conducted using an optical microscope for laser modified layer thickness and grain size and the hardness properties were measured using a Vickers indenter. Erosion occurred from the sample after 3500 cycles. The hardness of the laser treated layer was lowered, after a thermal fatigue test, from 650 HV0.1 to 510 HV0.1.These findings are important for designing high wear resistant surfaces through laser surface modification for applications forming semi-solid dies