Laser Surface Engineering Research Articles

Microstructure and wear resistance of the laser-cladded Al0.8CrFeCoNiCu0.5Bx high-entropy alloy coating on aluminum

Coatings with excellent mechanical properties are difficult to prepare on the aluminum alloy surfaces by laser surface engineering because of the low melting point and active chemical properties of aluminum (Al). Based on the unique entropy effect of a high-entropy alloy, we suppress the cracks in the cladding layer caused by the dilution ratio of the substrate, obtaining coatings exhibiting excellent wear resistance. The Al0.8CrFeCoNiCu0.5Bx coating exhibited a BCC1 + BCC2 + FCC phase when the x ≤ 0.1. When x ≥ 0.2, boride was formed in the Al0.8CrFeCoNiCu0.5Bx coatings, and it became the main phase of the Al0.8CrFeCoNiCu0.5B0.3 and Al0.8CrFeCoNiCuB0.4 coatings; however, no Al-rich intermetallic compound with a complex phase structure was formed. When 0 ≤ x ≤ 0.3, the bonding strengths of the Al0.8CrFeCoNiCu0.5Bx coatings were 70.6–176.2 MPa. An increase in the boron content increased the hardness of all the coatings, except the Al0.8CrFeCoNiCu0.5B0.3 coating. The hardness was 479–705 HV (6–9 times that of the substrate). The wear rate of the coating ranged from 1.50 × 10−7 to 1.19 × 10−5 mm3/Nm, which was only 0.01%–5.43% that of the substrate. The Al0.8CrFeCoNiCu0.5B0.2 coating exhibited the highest resistance to wearing, and its wear mechanism was identified as abrasive wear.

Influence of laser surface engineering of AISI P20-improved mold steel on wear and corrosion behaviors

The wear and corrosion characteristics of a mold steel (AISI P20-improved, KP4M) were investigated before and after the laser surface engineering. The laser surface engineering of AISI P20-improved steel was conducted at different laser energy densities by a high-power diode laser. The microstructure of the base metal changed from tempered martensite to lath-type martensite. In addition, the surface hardness was enhanced from 307 HV to 545, 657, and 610 HV when the laser energy density was 220, 315, and 420 J/mm2, respectively. An electron probe micro-analyzer revealed that microstructural homogenization was introduced by the laser surface engineering at 220 and 315 J/mm2, whereas an elemental segregation of chromium and manganese was observed with the laser surface engineering at 420 J/mm2 due to partial melting and solidification process. The laser surface-engineered samples showed an enhancement in the wear resistance in both the fretting and block-on-ring tests as compared to that of the base metal, and the highest wear resistance was detected for the laser surface-engineered at 315 J/mm2 owing to the largest increment in the hardness. In terms of corrosion resistance, the laser surface-engineered AISI P20-improved steel at 315 J/mm2 showed a marginal improvement in the corrosion resistance as compared to that of the base metal because of the microstructural homogenization. Contrastingly, a marginal deterioration of the corrosion resistance was examined for the laser surface-engineered AISI P20-improved steel at 420 J/mm2 because of the elemental segregation.

Optimization of biocompatibility in a laser surface treated Mg-AZ31B alloy.

Biodegradable bone implants can remove the need for subsequent bone-implant surgeries by controlled biomineralization and degradation. Although Mg-alloys generally possess biocompatible properties, they corrode rapidly, thereby preventing sufficient hydroxyapatite formation and biomineral growth. In an attempt to address these limitations, laser surface treatments were performed via the employment of a continuous wave Nd:YAG laser on the Mg-AZ31B alloy using laser fluences in the range of 1.06-4.24 J/mm2 (250-1000 W). The laser-treated samples were investigated for their wettability in simulated body fluid. In vitro analyses were performed in simulated body fluid to examine corrosion and biomineralization behavior on the laser-treated samples. Statistical optimization algorithms based on wettability data predicted an optimal laser fluence of 3.286J/mm2 (775 W) within the range of laser fluences used in the present study for achieving a balance between biodegradation and biomineralization. Confirmatory tests on optimized samples indicated an up to 84% grain size reduction in laser-treated surface regions, a several-fold increase in Mg17Al12 (β) phase volume fraction, a reasonably abundant formation of hydroxyapatite, and increased rates of biomineralization that exceeded degradation. These findings indicate the potential of laser surface engineering to realize Mg-AZ31B alloy as a viable biodegradable bone implant material.

Prominent Achievements of Laser Surface Treatment of Martensitic Stainless Steel and Alpha-Beta 6/4 Titanium Alloy

Conventional surface treatment processes are known to suffer from several limitations. Among them are energy consumption, complex heat treatment schedules and non-controllable heat affected zones. On the other side, when a high powered laser beam is used as a source of heat for surface treatment it will obviate most of these limitations. Laser surface engineering is one of these advanced surfacing technologies that receive growing interest to improve the surface properties of metals such as hardness, wear and corrosion resistance. Such treatments may be divided into two main categories: (i) those which only involve microstructural modification e.g. laser hardening and laser melting and (ii) other processes which lead to dual changes in microstructure and surface chemistry such as laser alloying and laser cladding. This paper comprises the experimental findings of two significant examples for laser surface engineering. The first study is concerned with surface hardening of AISI 416 martensitic stainless steel whereas the second study involves laser surface cladding of Ti-6Al-4V alloy. The outcome of the first work is a notable improvement of toughness at the same level of hardness and wear resistance as compared to the conventional hardening treatment. Additionally, the optimum condition for combined wear resistance, impact toughness and corrosion resistance was recorded at a laser heat input value of 21 J•mm-2. The second study is concerned with laser surface cladding of the titanium alloy with a powder blend composed of 60 wt% of WC and 40 wt% NiCrBSi alloy, by means of a high power Nd:YAG 2.2 kW laser. The best clad layers were obtained at a specific heat input of 60 J•mm-2. More than three-fold enhancement of the microhardness of the clad layers was achieved combined with a remarkable improvement of the alloy wear resistance.

Silica coated titanium using Laser Engineered Net Shaping for enhanced wear resistance

Laser Engineered Net Shaping (LENS™) was utilized to create novel silica (SiO2) coatings onto commercially-pure titanium (Cp-Ti). It was hypothesized that if silica could be deposited as a coating via laser surface engineering, high hardness and wear resistance could be added to existing Cp-Ti material. Post-deposition heat-treatments in the form of laser passes (LP) and a furnace residual-stress relief were completed on the coatings and mechanical/material properties were subsequently evaluated. Titanium silicide (Ti5Si3) formation and related dendritic microstructures were identified throughout the coating by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), scanning electron microscopic (SEM) analysis, and appeared more ordered after stress-relief heat treatment. High hardness values of approximately 1500 HV were measured at the coating’s topmost surface while specific wear rates showed a maximum 98% reduction from 346.2 × 10−6 mm3/N-m in the Cp-Ti substrate to 7.1 × 10−6 mm3/N-m in the heat treated 1 LP coating. In situ tribofilm formation was observed during wear, which indicated self-healing properties from the material and likely aided further in wear reduction. Our results show that silica coating on titanium via laser surface engineering could be used as a suitable manufacturing practice to create hard, Ti5Si3-reinforced ceramic coatings with high wear resistance and self-healing properties for applications ranging from biomedical to aerospace.

Problems on the development of hard and low friction in-situ coatings on Ti-6Al-4V using laser cladding

Coatings having high hardness and low coefficient of friction are significant for long service life of engineering components subjected to sliding wear. Some useful applications of such coatings are in various engine components including aerospace industries. Laser surface engineering has promising process characteristics for changing surface properties. In this concern, using laser cladding process hard and low friction coatings were developed on Ti-6Al-4V for improving sliding behavior of its components. To carry out the experimental investigations, the pre-placed powder mixture of B4C, hBN and Ti were used on the Ti-6Al-4V substrates and subsequently laser irradiated to form the improved surface properties. The coatings were developed with a wide range of laser scan speeds. Physical and mechanical characterizations of all samples were done rigorously. For some laser-scan-speeds in the range of studies, developed coatings resulted in very high hardness about 2200 HV. The dry sliding wear tests (against WC ball at 10 N loading) indicated a very low coefficient of friction of about 0.1 to 0.16 for the coatings. The problems experienced during development of the in-situ coatings are highlighted in the paper.

Laser Surface Engineering of Hierarchy Hydroxyapatite Aerogel for Bone Tissue Engineering

Bioceramics with porous microstructure has attracted intense attention in tissue engineering due to tissue growth facilitation in the human body. In the present work, a novel manufacturing process for producing hydroxyapatite (HA) aerogels with a high density shell inspired by human bone microstructure is proposed for bone tissue engineering applications. This method combines laser processing and traditional freeze casting, in which HA aerogel is prepared by freeze casting and aqueous suspension prior to laser processing of the aerogel surface with a focused CO2 laser beam that forms a dense layer on top of the porous microstructure. Using the proposed method, HA aerogel with dense shell was successfully prepared with a microstructure similar to human bone. The effect of laser process parameters on the surface, cross-sectional morphology and microstructure was investigated in order to obtain optimum parameters and has a better understanding of the process. Low laser energy resulted in a fragile thin surface with defects and cracks due to the thermal stress induced by the laser processing. However, increasing the laser power generated a thicker dense layer on the surface, free of defects. The range of 40–45 W laser power, 5 mm/s scanning speed, spot size of 1 mm, and 50% overlap in laser scanning the surface yielded the best surface morphology and microstructure in our experiments.

Enhancing the antibacterial performance of orthopaedic implant materials by fibre laser surface engineering

Implant failure caused by bacterial infection is extremely difficult to treat and usually requires the removal of the infected components. Despite the severe consequence of bacterial infection, research into bacterial infection of orthopaedic implants is still at an early stage compared to the effort on enhancing osseointegration, wear and corrosion resistance of implant materials. In this study, the effects of laser surface treatment on enhancing the antibacterial properties of commercially pure (CP) Ti (Grade 2), Ti6Al4V (Grade 5) and CoCrMo alloy implant materials were studied and compared for the first time. Laser surface treatment was performed by a continuous wave (CW) fibre laser with a near-infrared wavelength of 1064nm in a nitrogen-containing environment. Staphylococcus aureus, commonly implicated in infection associated with orthopaedic implants, was used to investigate the antibacterial properties of the laser-treated surfaces. The surface roughness and topography of the laser-treated materials were analysed by a 2D roughness testing and by AFM. The surface morphologies before and after 24h of bacterial cell culture were captured by SEM, and bacterial viability was determined using live/dead staining. Surface chemistry was analysed by XPS and surface wettability was measured using the sessile drop method. The findings of this study indicated that the laser-treated CP Ti and Ti6Al4V surfaces exhibited a noticeable reduction in bacterial adhesion and possessed a bactericidal effect. Such properties were attributable to the combined effects of reduced hydrophobicity, thicker and stable oxide films and presence of laser-induced nano-features. No similar antibacterial effect was observed in the laser-treated CoCrMo.

Formation of mixed and patterned self-assembled films of alkylphosphonates on commercially pure titanium surfaces

Titanium is extensively employed in biomedical devices, in particular as implant. The self-assembly of alkylphosphonates on titanium surfaces enable the specific adsorption of biomolecules to adapt the implant response against external stimuli. In this work, chemically-tailored cpTi surfaces were prepared by self-assembly of alkylphosphonate molecules. By bringing together attributes of two grafting molecules, aqueous mixtures of two alkylphosphonates were used to obtain mixed self-assembled films. Single self-assembled films were also altered by laser abrasion to produce chemically patterned cpTi surfaces. Both mixed and patterned self-assembled films were confirmed by AFM, ESEM and X-ray photoelectron spectroscopy. Water contact angle measurements also revealed the composition of the self-assembly films. Chemical functionalization with two grafting phosphonate molecules and laser surface engineering may be combined to guide the bone-like formation on cpTi, and the future biological response in the host.

Effect of rare earth oxide (Y2O3) addition on alloyed layer synthesized on Ti–6Al–4V substrate with Ti+SiC+h-BN mixed precursor by laser surface engineering

In this study, the rare earth oxide (Y2O3) is added to the precursor powder mixture of Ti+SiC+h-BN, and the subsequent mixture is alloyed on the surface of Ti–6Al–4V substrate by laser surface engineering. The XRD spectra indicate that the alloyed layers contain TiN, TiB, Si3N4, Ti5Si3, BN, Ti2N phases in the α-Ti matrix. It is found that the micro-hardness and wear resistance of alloyed layers with Y2O3 addition are higher than those of the alloyed layer without Y2O3 addition in their precursor. The micro-hardness of alloyed layer with Y2O3 addition enhanced from 583HV to 728HV.

Laser additive synthesis of high entropy alloy coating on aluminum: Corrosion behavior

High entropy alloy coatings were synthesized on aluminum substrate by laser surface engineering. Dilution from the substrate was minimized with the aid of multi layered coatings. Furthermore, higher laser input energy during processing lead to uniform mixing amongst the components resulting in formation of evenly distributed high entropy alloy phases throughout the matrix. This resulted in enhanced corrosion resistance for the coatings in near neutral NaCl solution.

Wear and corrosion behavior of laser surface engineered AISI H13 hot working tool steel

The present study reports the effect of laser parameters on the microstructure, and consequently, the wear resistance of laser surface engineered (hardening and melting) AISI H13 tool steel (in hardened and tempered condition) substrate. The microstructure of the laser surface hardened zone consists of ultrafine mixed carbides (M23C6, M7C3, MC or M2C) dispersed between martensite laths. On the other hand, a laser surface melted microstructure comprises retained austenite, martensite, transformed ledeburite and fine carbides precipitated in the inter-dendritic zone. Microhardness of the laser surface engineered zone is significantly enhanced to as high as 670–810 VHN as compared to 480–500 VHN of the as received quenched and tempered substrate and decreases along vertical depth from the surface until a narrow soft zone at the interface with a typical hardness of 440 VHN. Laser surface melting yields a higher hardness level (770±10 VHN) as compared to that after laser surface hardening (660±10 VHN). Wear resistance of laser surface engineered samples (evaluated both by ball-on-disk and fretting wear testing equipments) shows a significant improvement as compared to that in hardened and tempered condition. Due to an increased hardness, surface melting shows superior resistance to wear both under fretting as well as ball on disk wear testing conditions. A marginal improvement in corrosion resistance was also recorded in laser surface engineered samples due to microstructural/compositional homogenization introduced by laser surface engineering.

Effect of pulse laser parameters on TiC reinforced AISI 304 stainless steel composite coating by laser surface engineering process

In this work, TiC reinforced steel composite layer has been produced by laser scanning over the preplaced TiC powder on AISI 304 steel substrate, using a pulse Nd:YAG laser. Depending on the pulse laser parameters, TiC either deposited or dispersed on the surface of steel substrate. Depth and width of laser processed TiC–steel composite layer has been deliberated from the SEM images at the transverse cross section of the laser scanned samples. Hardness of the laser processed composite layer has been measured through Vickers micro-hardness tester. Effect of pulsed laser parameters i.e. peak power, pulse duration, overlapping factor (corresponding to scan speed and frequency) on micro-hardness, composite layer profile (depth and width) and microstructure of the laser processed TiC–steel composite layer has been studied. From the experimental analysis, it is revealed that, laser peak power and overlapping factor have significant effect on the TiC–steel composite layer profile and its hardness value.

Application of laser surface engineering to solve tribological problems

The methods of laser surface engineering, including laser cladding, laser alloying from predeposited layers, and laser alloying from the gas phase have been applied to increase the wear resistance and decrease the coefficient of friction of metallic surfaces. Laser cladding has been applied to deposit metal matrix composites that consist of CuSn, stellite, stainless steel, and bronze, which act as solid lubricant reinforced with nanostructured WC ceramics with Co binding. Laser alloying of bearing steel with Sn increases the lifetime of oil turbo drills. Wear tests of Ti alloys doped with nitrogen from a gas atmosphere have demonstrated a viable possibility to apply the developed method to fabricate frictional couples.

Hard TiC Coating on AISI304 Steel by Laser Surface Engineering Using Pulsed Nd:YAG Laser

The surface mechanical property of AISI304 stainless steel was improved by TiC coating deposited through laser surface engineering process using a pulsed Nd:YAG laser. The produced coating exhibited significantly higher hardness (650–1900 HV0.1) compared to the steel substrate (190 HV0.1). Coating thickness, dilution of TiC on substrate surface, and hardness of the coating were determined using various pulse laser processing parameters, i.e., peak power and pulse frequency. At low pulse frequency and peak power condition, relatively thick and uniform coating of TiC was deposited over the substrate. However, at higher pulse frequency and peak power condition, TiC-dispersed steel composite coating was produced.

Laser assisted high entropy alloy coating on aluminum: Microstructural evolution

High entropy alloy (Al-Fe-Co-Cr-Ni) coatings were synthesized using laser surface engineering on aluminum substrate. Electron diffraction analysis confirmed the formation of solid solution of body centered cubic high entropy alloy phase along with phases with long range periodic structures within the coating. Evolution of such type of microstructure was a result of kinetics associated with laser process, which generates higher temperatures and rapid cooling resulting in retention of high entropy alloy phase followed by reheating and/or annealing in subsequent passes of the laser track giving rise to partial decomposition. The partial decomposition resulted in formation of precipitates having layered morphology with a mixture of high entropy alloy rich phases, compounds, and long range ordered phases.

Enhancement of endothelialisation of coronary stents by laser surface engineering

Coronary stents have been widely used in the treatment of coronary heart disease. However, complications have hampered the long-term success of the device. Bare-metal stents (BMS) have a high rate of restenosis and poor endothelialisation. The drug-eluting stents (DES), although dramatically reduce restenosis, significantly prevent endothelialisation leading to late thrombosis and behave the same way as BMS after drug releasing. Rapid adhesion and growth of endothelial cells on the stent surface is a key process for early vascular healing after coronary stenting which contributes to the reduction of major complications. Surface properties manipulate cell growth and directly determine the success and life-span of the implants. However, the ideal surface properties of coronary stents are not yet fully understood. The objective of this research is to understand how surface micro/nano textures and associated material chemistry changes generated by a laser beam affect the behavior of endothelial cells on bare metal 316L stents. A high power laser beam was applied to modifying the surface properties of 316L coronary stent material and the commercial coronary stents, followed by examination of the adhesion and proliferation of human coronary endothelial cells that were growing on the surfaces. Surface properties were examined by scanning electron microscopy, contact angle measurement, and X-ray photoelectron spectroscopy. A novel surface with combined micro/nano features was created on stent material 316L and coronary stent with a specific surface chemistry. This surface gives rise to a threefold increase in the adhesion and eightfold increase in the proliferation of endothelial cells. Interestingly, such effects were only observed when the surface texture was produced in the nitrogen atmosphere suggesting the importance of the surface chemistry, including the dramatic increase of chromium nitride, for the interaction of endothelial cells with the material surface. This novel surface is also super-hydrophilic with close to zero water/cell culture fluid contact angles and low cytotoxicity. A novel surface created by laser surface-engineering with a combination of defined surface texture and surface chemistry was found beneficial for the improvement of coronary stent endothelialisation. The technology presented here could work with both DES and BMS with added benefit for the improvement of the biocompatibility of current coronary stents.

Cladding of Advanced Al Alloys Employing Friction Stir Welding

Friction stir welding (FSW) is a relatively new solid-state joining technology for metals. It shows no solidification-related joint imperfections which makes it utmost suitable for hard-to-weld highly alloyed aerospace aluminium grades, like AA 2xxx and AA 7xxx. These alloys are often cladded with a thin layer of pure aluminium for corrosion protection. Friction stir welding of such materials requires removal of the clad layer prior to welding to prevent weakening of the joint by the soft clad material. This leaves the welded region vulnerable to corrosion after the joining process. Post-weld restoration of the clad layer is required to restore the protective action of the clad layer and as such to enhance the life expectancy of the welded construction. In this work the deposition of thin layers of pure aluminium on AA 2xxx and AA 7xxx alloys is studied employing an innovative FSW tool. The tool shoulder is equipped with strategically placed internal channels that allow delivery of filler type of material into the weld zone. Depending on the channel architecture used, filler material can be deposited on top of the work piece surface and/or mixed with the work piece surface region. The cladding is done in the solid state avoiding many problems with solidification and interface reactivity often observed with other surface modification techniques, such as laser surface engineering, plasma spraying or casting. Here, the filler material is deposited on top of the work piece; the modified tool is not equipped with a tool pin. The work comprises an in depth study of the influence of process conditions on the microstructural changes in the underlying work piece and on the quality of the bonding of the clad material (99.5 % aluminium) to the work piece material. Apart from the usual process conditions, such as tool rotation speed, translation speed, down force and tool angle also the delivery pressure and rate of the filler supply system can be varied. The influence of the usual process conditions on the microstructure of the underlying work piece is similar to that observed with “traditional” FSW. Changes in hardness can be related to the amount of heat generated by the welding process. Shape and dimensions of the microstructural zones found are typical for welds made without a tool pin. The effect of the small amount of clad material deposited on top of the work piece on the temperature distribution is small. The amount of heat required to heat it up is negligible to the heat required to heat up the work piece and the tool. The quality of the bonded clad layer is dependent on the amount of heat and plastic deformation generated at the interfaces between the tool, the filler material and the work piece. Tool angle, tool shape and supply rate of the filler supply system determine the layer thickness.

Recent Developments in Surface Engineering of Materials

Engineering approaches to improve surface properties such as surface finish/appearance, hardness/strength, wear resistance, corrosion resistance, environment resistance, and heat resistance have been known since prehistoric times. The manufacturing of several ancient objects can often be traced to processes like surface painting (use of natural pigments), machining (use of sandstone, bone, and metal tools), and heat treatments (use of soybean grains for carbonitriding of steel). While most of the modern surface engineering approaches have evolved from these processes, the past century has also witnessed rapid development of newer processes based on electroplating, thermal spraying, directed beam (ion, laser, and electron) processing, and cold spraying. These processes are now utilized for depositing a range of nanostructured, amorphous, or composite materials for multiple functionalities (hardness/wear resistance, strength/ toughness, corrosion resistance, heat/environment resistance, biocompatibility and cell adhesion, and hydrophobicity). Surface engineering is a very active area, introducing regular developments on various fronts, including fundamental research, technology development, and extension in newer applications. Some of these developments were captured at the symposium Advances in Surface Engineering: Alloyed and Composite Coatings II at the TMS 2013 Annual Meeting (San Antonio, TX; March 3–7, 2013). This symposium was sponsored by the Surface Engineering Committee of the TMS Materials Processing & Manufacturing Division (MPMD) and was partially funded by the U.S. Office of Naval Research (ONR). The symposium featured 59 presentations including 14 invited talks and several student presentations. This was a well-attended, hugely successful symposium, with discussions resulting in an important direction for the future activities of the committee. Most of the recent surface engineering developments discussed in the TMS 2013 symposium are highlighted in the articles published in this JOM issue. These articles represent the current state-ofthe-art and indicate emerging areas in surface engineering. In ‘‘Advances in Laser Surface Engineering: Tackling the Cracking Problem in Laser Deposited Ni-Cr-B-Si-C Alloys,’’ I. Hemmati et al. examine the idea of microstructural refinement for reducing the cracking tendency of Ni-Cr-B-Si-C alloys deposited by laser cladding. This work indicates that effective toughening of these alloys could not be reached solely by refinement of the hard precipitates and that the modification of the eutectic structure or disruption of its continuous network is needed. In ‘‘Nanomechanical Properties and Thermal Conductivity Estimation of Plasma Sprayed Solid Oxide Fuel Cell Components: Ceria Doped Yttria Stabilized Zirconia Electrolyte,’’ N. Mahato et al. demonstrated layered fabrication of solid oxide fuel cell (SOFC) components using an atmospheric plasma spraying method. The nanomechanical behavior of the deposited SOFC composite layers is evaluated. In ‘‘Characterization of Nanostructured and Ultrafine Grain Aluminum-Silicon Claddings using the Nano-Impact Indentation Technique,’’ J. Arreguin-Zavala et al. report that dynamic hardness of the material becomes independent of load using a nano-impact indentation technique. Their analysis shows that better correlation can be established between dry sliding wear and dynamic hardness. In ‘‘Abnormal Nitride Morphologies upon Nitriding Iron-Based Substrates,’’ Sai Ramudi Meka and Eric Jan Mittemeijer provide an overview of different nitride morphologies formed upon Sandip P. Harimkar, Chair of the Surface Engineering Committee of the TMS Materials Processing & Manufacturing Division (MPMD); Srinivasa Rao Bakshi, Vice Chair of the Surface Engineering Committee of TMS; and Arvind Agarwal are the JOM advisors for the Surface Engineering Committee. JOM, Vol. 65, No. 6, 2013

Advances in Laser Surface Engineering: Tackling the Cracking Problem in Laser-Deposited Ni-Cr-B-Si-C Alloys

Laser-deposition technologies are being increasingly used for surface modification and three-dimensional manufacturing applications. The biggest technical obstacle to a wider usage of these technologies especially for deposition of hard alloys is cracking of the deposited samples. In this work, the idea of microstructural refinement as a toughening mechanism for Ni-Cr-B-Si-C alloys deposited by laser cladding is evaluated and a new idea for reducing the cracking tendency of these alloys is proposed. The results show that although a significant refinement of the Cr-rich precipitates in these alloys could be induced by a suitable addition of Nb, the cracking susceptibility of the deposits was unchanged. This was so because the continuous network of hard eutectics was still providing an easy route for crack growth. The outcome of this work shows that an effective toughening mechanism for these alloys should include not only a refinement of the hard precipitates but also modification of the eutectic structure.