J. Dutta Majumdar

Laser processing of materials

Light amplification by stimulated emission of radiation (laser) is a coherent and monochromatic beam of electromagnetic radiation that can propagate in a straight line with negligible divergence and occur in a wide range of wave-length, energy/power and beam-modes/configurations. As a result, lasers find wide applications in the mundane to the most sophisticated devices, in commercial to purely scientific purposes, and in life-saving as well as life-threatening causes. In the present contribution, we provide an overview of the application of lasers for material processing. The processes covered are broadly divided into four major categories; namely, laser-assisted forming, joining, machining and surface engineering. Apart from briefly introducing the fundamentals of these operations, we present an updated review of the relevant literature to highlight the recent advances and open questions. We begin our discussion with the general applications of lasers, fundamentals of laser-matter interaction and classification of laser material processing. A major part of the discussion focuses on laser surface engineering that has attracted a good deal of attention from the scientific community for its technological significance and scientific challenges. In this regard, a special mention is made about laser surface vitrification or amorphization that remains a very attractive but unaccomplished proposition.

Laser material processing

Abstract Light amplification by stimulated emission of radiation (laser) is a coherent and monochromatic source of electromagnetic radiation that can propagate in a straight line with negligible divergence. As a result, laser finds diverse applications ranging from mere mundane to most sophisticated uses either for totally commercial or purely scientific purposes, and from life saving to life threatening causes. High power lasers can produce intense heating and perform various manufacturing operations or material processing. The present contribution provides an overview of the application of high power laser only for material processing in engineering applications, and intentionally excludes the scope of application of laser in metrology, biomedical technology, spectroscopy, etc. The manufacturing processes covered have been broadly divided into four major categories, namely, laser assisted forming, joining, machining and surface engineering. Besides discussing the scope and principle of these processes, each section enumerates a detailed update of literature, scientific issues and technological innovations. At the beginning, a brief introduction to different types of lasers and their general applications, fundamentals of laser–matter interaction and classification of laser material processing has been provided. The entire discussion primarily focuses on correlating the properties with processing parameters and microstructure and composition of the material.

Laser surface engineering of a magnesium alloy with Al+Al2O3

The present study concerns an attempt to improve the wear resistance of a commercial magnesium alloy, MEZ (rare earth 2 wt.%, Zn 0.5 wt.%, Mn 0.1 wt.%, Zr 0.1 wt.%) by dispersion of Al2O3 particles and alloying with aluminium on the surface by laser surface engineering. Laser processing was carried out with a 10-kW continuous wave CO2 laser by melting and subsequent feeding of Al+Al2O3 particles (in the ratio of 3:1) on the surface of MEZ. Following laser processing, a detailed microstructural and phase analysis of the surface modified layer were carried out. The microhardness of the surface layer was measured as a function of laser parameters and wear resistance property was evaluated in details. Microhardness of the surface layer was significantly improved to as high as 350 VHN as compared to 35 VHN of the substrate. The optimum processing region for formation of a homogeneous microstructure and composition for laser surface modification of MEZ with Al+Al2O3 was established. The wear resistance of the laser surface modified samples was considerably improved as compared to the as-received specimen.

Friction and wear behavior of Ti following laser surface alloying with Si, Al and Si+Al

Abstract This study concerns the friction and wear behavior of Ti following laser surface alloying (LSA) with Si, Al or Si+Al. The said tribological characteristics of the laser-alloyed samples, subjected to the earlier determined optimum conditions of LSA, were investigated in terms of the variation of wear depth as a function of load and time using a computer-controlled reciprocating ball-on-disc wear testing machine fitted with an oscillating hardened steel ball. A detailed post wear microstructural analysis was conducted to determine the mechanism of wear and role of alloying elements in improving the resistance to wear. It appears that LSA with Si is more effective in improving the wear resistance of Ti than that by Si+Al or Al alone. The enhanced wear resistance in Si surface alloyed samples has been attributed to the presence of uniformly distributed Ti 5 Si 3 in the alloyed zone (AZ).

Laser composite surfacing of a magnesium alloy with silicon carbide

The present study concerns an attempt to improve the wear resistance of a recently developed magnesium alloy (MEZ) by formation of a SiC reinforced composite layer on the surface by laser surface engineering. Laser processing was carried out with a 10 kW continuous wave CO 2 laser by melting and subsequent feeding of SiC particles on the surface of MEZ. Following laser processing, detailed microstructural and phase analysis of the composite surfaced layer were carried out and correlated with the laser parameters. The microhardness of the surface layer was measured as a function of laser parameters and wear resistance was evaluated in details. Microstructure of the composite surfaced layer mainly consists of uniform dispersion of SiC particles in grain refined MEZ matrix. The volume fraction of SiC particles was found to vary with laser/process parameters. Microhardness of the surface layer was significantly improved to as high as 270 VHN as compared to 35 VHN of the substrate. The wear resistance of the composite surfaced samples was considerably improved as compared to the as-received specimen.

Laser surface alloying of Ti with Si, Al and Si+Al for an improved oxidation resistance

This study concerns laser surface alloying (LSA) of Ti with Si, Al or both to enhance the oxidation resistance of pure Ti. A detailed investigation on the effect of process parameters (laser power, interaction time, etc.) on microstructure, composition, phase distribution and hardness was carried out to determine the optimum LSA conditions to form a crack-free and uniform alloyed zone (AZ). Following LSA under such optimum conditions, the kinetics and mechanism of cyclic oxidation behavior between room temperature and 923:1023 K were extensively studied to identify the scope and role of Si and Al in enhancing the oxidation resistance of the substrate. It appears that LSA with Si or Si Al is more effective than that with Al alone in improving oxidation resistance of Ti. This enhanced oxidation resistance has been attributed to the presence of uniformly distributed Ti5Si3 in the AZ underneath a SiO2:Al2O3 rich superficial oxide scale.

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

Abstract The present study concerns laser surface alloying (LSA) of AISI 304 stainless steel (304-SS) with predeposited Mo (by plasma spraying) to enhance pitting and erosion–corrosion resistance of the substrate. A parametric correlation between the alloyed zone (AZ) depth ( w ) vis-a-vis incident laser power density ( Q ) and linear scanning speed ( v ) indicates that w is directly related to Q but varies inversely with v . Both microstructure and chemistry of the AZ are strong functions of the LSA parameters. LSA seems to improve the microhardness level in the AZ by 2–3 times that of the substrate. The optimum LSA conditions in terms of predeposit thickness, Q and v have been identified to achieve the desired microstructure, composition and mechanical properties. LSA under such optimum conditions significantly improves the pitting corrosion resistance in terms of critical potential for pit formation ( E PP1 ) and pit growth ( E PP2 ). In addition, the erosion–corrosion resistance in 20 wt.% sand in 3.56 wt.% NaCl solution registers a marked improvement. Thus, it is concluded that LSA of 304-SS with Mo is an appropriate technique to enhance the resistance to pitting and erosion–corrosion in stainless steel.

Laser surface alloying of copper with chromium: I. Microstructural evolution

Abstract Laser surface alloying (LSA) of Cu with pre-deposited Cr has been carried out using a high power continuous wave CO 2 laser. Following LSA, the surface microstructure and composition have been correlated with the laser processing parameters. It is found that a judicious selection of laser power density ( Q ) and scan speed ( v ) (or interaction time, t i ) is essential to obtain a defect-free and uniform alloyed zone (AZ) for a given pre-deposit thickness ( t z ). The AZ-depth is directly related to Q and t i . Microstructurally, the AZ consists of dispersed Cr-rich particles in the Cr-alloyed Cu-rich solid solution. Rapid quenching in the present LSA routines has extended the solid solubility of Cr in Cu to about 4 at.%. The total Cr content in the AZ varies inversely with Q and t i for a given t z . Finally, a process optimization diagram has been constructed to predict the microstructure and composition of the AZ for the present system for different conditions of LSA.

High-Temperature Oxidation Behavior of Laser-Surface-Alloyed Ti with Si and Si + Al

This study concerns an attempt to enhance the resistance to high-temperature isothermal and cyclic oxidation of Ti in dry air by laser-surface alloying (LSA) with Si and Si+Al. LSA was carried out by codeposition of alloy powders during lasing under the predetermined, optimum-processing routine that ensured formation of a compact, well-adherent, crack-free and homogeneous alloyed zone. The results of oxidation kinetics in the temperature range 950–1150 K for 1–400 hr indicate that surface alloying with Si imparts excellent oxidation resistance up to 1050 K. However, at a higher temperature of 1150 K, surface alloying with 3Si+Al yields a better resistance to oxidation. A detailed characterization of the microstructure and distribution of the phases within the scale and alloyed zone following oxidation studies has been undertaken to suggest the possible mechanism for enhanced oxidation resistance of Ti imparted by laser-surface alloying.

Microstructure and mechanical properties of nano-Y2O3 dispersed ferritic steel synthesized by mechanical alloying and consolidated by pulse plasma sintering

Ferritic steel with compositions 83.0Fe–13.5Cr–2.0Al–0.5Ti (alloy A), 79.0Fe–17.5Cr–2.0Al–0.5Ti (alloy B), 75.0Fe–21.5Cr–2.0Al–0.5Ti (alloy C) and 71.0Fe–25.5Cr–2.0Al–0.5Ti (alloy D) (all in wt%) each with a 1.0 wt% nano-Y2O3 dispersion were synthesized by mechanical alloying and consolidated by pulse plasma sintering at 600, 800 and 1000°C using a 75-MPa uniaxial pressure applied for 5 min and a 70-kA pulse current at 3 Hz pulse frequency. X-ray diffraction, scanning and transmission electron microscopy and energy disperse spectroscopy techniques have been used to characterize the microstructural and phase evolution of all the alloys at different stages of mechano-chemical synthesis and consolidation. Mechanical properties in terms of hardness, compressive strength, yield strength and Youngs modulus were determined using a micro/nano-indenter and universal testing machine. All ferritic alloys recorded very high levels of compressive strength (850–2850 MPa), yield strength (500–1556 MPa), Youngs modulus (175–250 GPa) and nanoindentation hardness (9.5–15.5 GPa), with up to 1–1.5 times greater strength than other oxide dispersion-strengthened ferritic steels (<1200 MPa). These extraordinary levels of mechanical properties can be attributed to the typical microstructure of uniform dispersion of 10–20-nm Y2Ti2O7 or Y2O3 particles in a high-alloy ferritic matrix.