Texture and its effect on mechanical properties in fiber laser weld of a fine-grained Mg alloy

A fine-grained Mg alloy was fiber-laser welded, and microstructures and texture in the welds were extensively examined, together with the effect on mechanical properties. Fusion zone, which has lower hardness than BM and HAZ, consists of columnar grain zone and equiaxed grain zone with coarser grains. Strong texture with the same orientation as base metal forms at columnar grain zone. With decreasing welding heat input, yield strength of the welded joint increases due to the finer microstructures; however, ultimate tensile strength as well as elongation decreases because of the deterioration in deformation capacity induced by the diminishment of the width of equiaxed grain zone.     

Influence of SiC, Si3N4 and Al2O3 particles on the structure and properties of electrodeposited Ni

The structure and properties of electrodeposited nickel composites reinforced with inert particles like SiC, Si₃N₄ and Al₂O₃ were compared. A comparison was made with respect to structure, morphology, microhardness and tribological behaviour. The coatings were characterized with optical microscopy, Scanning electron microscopy (SEM), Energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) technique. The cross-sectional microscopy studies revealed that the particles were uniformly distributed in all the composites. However, a difference in the surface morphology was revealed from SEM studies. The microhardness studies revealed that Si₃N₄ reinforced composite showed higher hardness compared to SiC and Al₂O₃ composite. This was attributed to the reduced crystallite size of Ni — 12 nm compared to 16 nm (SiC) and 23 nm (Al₂O₃) in the composite coating. The tribological performance of these coatings studied using a Pin-on-disk wear tester, revealed that Si₃N₄ reinforced composite exhibited better wear resistance compared to SiC and Al₂O₃ composites. However, no significant variation in the coefficient of friction was observed for all the three composites.     

Phase transformation in semi-transparent TiO2 films irradiated with CO2 laser

Anatase (TiO₂) thin films were obtained by immersion of glass plates into a titanium sol-gel precursor followed by calcination at 450 °C for 3 h. The Raman results for the CO₂ laser irradiated TiO₂ films show that laser radiation is able to promote favorable changes of anatase phase in anatase/rutile mixtures. Nevertheless, the transformation process level depends on laser characteristics and scan speed of the radiation treatment.     

Non-melting annealing of silicon by CO2 laser

In this work we investigate CO₂ laser annealing at millisecond time scale for the fabrication of Ultra Shallow Junctions, able to fulfill the requirements imposed for sub-45 nm CMOS nodes. Silicon samples doped with Boron using BF₃ plasma implantation technique at low energy (0.4 and 0.6 keV) were used to ensure ultra shallow as implanted boron concentration profiles. Our aim is to achieve high electrical activation level of the dopant, while maintaining the Boron concentration profile as immobile as possible. Samples have been irradiated at a variety of annealing conditions regarding the duration of the irradiation and the power density; however, in every case the peak surface temperature was kept in the range of 1080-1320 °C. Sheet resistance measurements indicate significant enhancement in the activation levels, while chemical characterization by means of SIMS, shows very limited movement of the dopant concentration profile, especially for short pulse duration conditions.     

Hardfacing characteristics of S42000 stainless steel powder with added silicon nitride using a CO2 laser

This study examined hardfaced cladding of S42000 stainless steel powder with added silicon nitride Si₃N₄ on a medium carbon steel using a 1200-W CO₂ laser. Experimental results indicated that a well-proportioned cladding layer was obtained with an overlap of 50% at a traverse speed of 5 mm/s and a powder feed rate of 2 g/min. The degree of dilution, depth/width (D/W) ratio and microhardness of the cladding layer was increased by adding up to 5 wt.% silicon nitride. Retained austenite and wear decreased with increasing amounts of silicon nitride addition. The silicon nitride decomposed in the cladding layer during the laser treatment.     

Structural and mechanical properties of ZrN films prepared by ion beam sputtering with varying N2/Ar ratio and substrate temperature

Zirconium nitride (ZrN) films were deposited by ion beam sputtering technique on stainless steel 304 substrates using a mix of (Ar+N₂) gas. In this paper, the effects of N₂/(N₂+Ar) flow ratio (F(N₂)) and substrate temperature on the microstructure and microscopic properties of the deposited films were investigated. The phase and the morphology were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively; moreover, the composition depth profile of ZrN was obtained using secondary ion mass spectroscopy (SIMS). In a wide range of F(N₂) (10-54%), the intensity of (1 1 1) peak increased which was the preferred orientation, while for F(N₂) more than 54% the ZrN peak intensity was decreased and the amorphous structure was formed at 95%. The XRD patterns presented a texture change due to the processing temperature, which was varied within the range 200-550 °C. At 400 °C, the (1 1 1) crystalline plane intensity was higher than the other ones, leading to the presence of a preference for this orientation. Good planarity of the deposited films was confirmed by SEM, it did not reveal any undulations, fractures, or cracking. The Vickers micro-hardness tester with a load of 25 g was used to measure the hardness of the films. The results showed that the structural and mechanical properties were strongly influenced by nitrogen ratio and substrate temperature.     

Microstructures and mechanical properties of friction stir welds on 9% Cr reduced activation ferritic/martensitic steel

In this study,the microstructures and mechanical properties of 9%Cr reduced activation ferritic/martensitic(RAFM) steel friction stir welded joints were investigated.When a W-Re tool is used,the recommended welding parameters are 300 rpm rotational speed,60 mm/min welding speed and10 kn axial force.In stir zone(SZ),austenite dynamic recrystallization induced by plastic deformation and the high cooling rates lead to an obvious refinement of prior austenite grains and martensite laths.The microstructure in SZ contains lath martensite with high dislocation density,a lot of nano-sized MX and M_3C phase particles,but almost no M_(23)C_6 precipitates.In thermal mechanically affect zone(TMAZ)and heat affect zone(HAZ),refinement of prior austenite and martensitic laths and partial dissolution of M_(23)C_6 precipitates are obtained at relatively low rotational speed.However,with the increase of heat input,coarsening of martensitic laths,prior austenite grains,and complete dissolution of M_(23)C_6 precipitates are achieved.Impact toughness of SZ at-20?C is slightly lower than that of base material(BM),and exhibits a decreasing trend with the increase of rotational speed.     

The effect of bond coat on mechanical properties of plasma-sprayed Al2O3 and Al2O3-13 wt% TiO2 coatings on AISI 316L stainless steel

In this study, Al₂O₃ and Al₂O₃-13 wt% TiO₂ were plasma sprayed onto AISI 316L stainless-steel substrate with and without Ni-5 wt% Al as bond coat layer. The coated specimens were characterized by optical microscopy, metallography and X-ray diffraction (XRD). Bonding strength of coatings were evaluated in accordance with the ASTM C-633 method. It was observed that the dominant phase was Al₂O₃ for both coatings. It was also found that the hardness of coating with bond coat was higher than that of coating without bond coat. Metallographic studies revealed that coating with bond coating has three different regions, which are the ceramic layer (Al₂O₃ or Al₂O₃-13 wt% TiO₂), the bond coating, and matrix, which is not affected by coating. The coating performed by plasma-spray process without bond coating has two zones, the gray one indicating the ceramic layer and the white one characterizing the matrix. No delamination or spalling was observed in coatings. However, there are some pinholes in coating layer, but they are very rare. The bonding strength of coatings with bond coat was higher than that of coating without bond coat. The strength of adhesion and cohesion was determined by means of a planemeter. It was seen that percentage of cohesion strength was higher than that of adhesion strength.     

Pulsed laser deposition of La0.67Ca0.33MnO3 thin films on LiNbO3 and surface acoustic wave studies

Surface Acoustic Waves on piezoelectric substrates can be used to investigate the dynamic conductivity of thin films in a non-contact and very sensitive way, especially at low conductivities. Here, we report on such surface acoustic wave studies to characterize thin manganite film like La_0.67Ca_0.33MnO₃, exhibiting a Jan Teller effect with a strong electron phonon interaction and a metal insulator transition at high temperatures.

We report on the deposition of La_0.67Ca_0.33MnO₃ on piezoelectric substrates (LiNbO₃ in different crystal cuts, employing a pulsed laser deposition technique. The structural quality of the thin films are examined by X-Ray Diffraction, Scanning Electron Microscope and Energy Dispersive X-ray spectroscopy. For the electrical characterization, we employ the surface acoustic wave technique, accompanied by conventional direct current resistance measurements for comparison.     

Microstructure and mechanical properties of friction stir welded 18Cr–2Mo ferritic stainless steel thick plate

In this study, microstructure and mechanical properties of a friction stir welded 18Cr–2Mo ferritic stainless steel thick plate were investigated. The 5.4 mm thick plates with excellent properties were welded at a constant rotational speed and a changeable welding speed using a composite tool featuring a chosen volume fraction of cubic boron nitride (cBN) in a W–Re matrix. The high-quality welds were successfully produced with optimised welding parameters, and studied by means of optical microscopy (OM), scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD) and standard hardness and impact toughness testing. The results show that microstructure and mechanical properties of the joints are affected greatly, which is mainly related to the remarkably fine-grained microstructure of equiaxed ferrite that is observed in the friction stir welded joint. Meanwhile, the ratios of low-angle grain boundary in the stir zone regions significantly increase, and the texture turns strong. Compared with the base material, mechanical properties of the joint are maintained in a comparatively high level.     

CO2 laser annealing of plasma-deposited high-Tcsuperconducting thick films

Recent advances in the fabrication of high-T _c superconducting thick films demand processing techniques which can eliminate film/substrate interdifiusion that occurs during subsequent post-annealing heat treatment after the film is deposited, thereby limiting the application of the thick films for devices. The present study evaluates laser annealing techniques for plasma-deposited Y-Ba-Cu-O thick films using a high-energy CO₂ laser (10.6m) in a continuous wave mode. The results are compared with those obtained by conventional furnace annealing techniques necessary for post-heat treatment of as-deposited superconducting thick films. The high-T _c superconducting phase is recovered by cationic diffusion during subsequent post-annealing heat treatment. Crystallographic phases and microstructural characterization have been performed using XRD, SEM, and EPMA analytical techniques. The significance of the technology lies in the elimination of film/substrate interdiffusion problems, thereby resulting in high-quality superconducting thick films. The technology will significantly reduce the post-annealing times usually required by conventional furnace annealing techniques.     

Deposition and characterisation of MoSi2 films

Deposition of MoSi₂ films on silicon and tantalum substrates applying pulsed laser deposition technique has been performed. Crystalline, hexagonal symmetry, MoSi₂ films were prepared directly from stoichiometric MoSi₂ tetragonal target on room temperature and heated substrates (500 °C). Textured MoSi₂ films having privileged (110) and (115) orientations and average crystallite size of about 105 nm were grown on Si(111) substrates with a good degree of axial texture (rocking curve full width half maximum of 1.5°). MoSi₂ films grown on Ta(211) substrates, instead, turned out to be polycrystalline, with an average crystallite size of about 100 nm and 50 nm on substrates kept at room temperature and at 500 °C, respectively. Vickers hardness for 1.2 μm thick MoSi₂ films on Si(111) substrates resulted to be 15 GPa both at room temperature and 500 °C, while for 0.4 μm thick MoSi₂ films on Ta(211) substrates — 26 GPa at room temperature and 30 GPa at 500 °C.     

Carbide precipitates and mechanical properties of medium Mn steel joint with metal inert gas welding

Medium Mn steel was metal inert gas(MIG)welded with NiCrMo-3 and 307Si filler wires.The effect of filler wires on the microstructure and mechanical properties of joint was investigated,and the carbide precipitates were contrastively discussed.The results revealed that the microstructure of weld metal,heat-affected zone and base metal are austenite.Obvious grain coarsening occurred in the heat-affected zone(HAZ),and the maximum grain size grew up to 160 pm.In HAZ,C and Cr segregated at grain boundaries,the carbides was identified as Cr7C3.The dispersive(Nb,Mo)C phase was also found in weld metal with NiCrMo-3 filler wire.All the welded joints failed in HAZ during tensile tests.The tensile strength of welded joint with NiCrMo-3 filler wire was 675 MPa,which is much higher than that with 307Si filler wire.In comparison to base metal,higher microhardness and lower impact toughness were obtained in HAZ for these two welded joints,which was attributed to the precipitation of Cr7C3 phase and grain coarsening.The impact toughness around the fusion line is the worst for these two welded joints.     

Optimization of deposition temperature and atmosphere for pulsed laser deposited Sr2FeMoO6 thin films

Double perovskite Sr₂FeMoO₆ films were deposited by pulsed laser deposition at a wide temperature range and different atmospheres. The best films with T_C = 340-370 K and low temperature magnetization of around 2.2 μ_B/f.u. were deposited at 1050 °C with 9 Pa Ar/5%H₂ atmosphere. X-ray diffraction showed no impurities and full texturization of all the films. Atomic force microscopy revealed increasing surface roughness with increasing deposition temperature.     

Microstructure and mechanical properties of hot pressed ZrB2-SiCp-ZrO2 composites

The present paper investigated the microstructure and mechanical properties of ZrB₂-10 vol.%SiC_p-10 vol.%ZrO₂ composites hot pressed at three temperatures. Phase transformability from t-ZrO₂ to m-ZrO₂ during fracture was analyzed through calculating the volume fractions of m-ZrO₂ and t-ZrO₂ on polished and fracture surfaces. The densification temperature was found to have a significant effect on the microstructure, phase transformation and the properties of the composites. When the composite was hot pressed at 1950 °C, the average grain size was 9.5 µm, and the fracture toughness was 4.5 MPa·m^1/2. Comparatively, when the composite was hot pressed at 1750 °C, the average grain size was 3.4 µm, and the fracture toughness increased by ~ 50% to 6.8 MPa·m^1/2.     

Microstructures and mechanical properties of Al/Al2O3 surface nano-composite layer produced by friction stir processing

In this study, a new processing technique, friction stir processing (FSP) was attempted to incorporate nano-sized Al₂O₃ into 6082 aluminum alloy to form particulate composite surface layer. Samples were subjected to various numbers of FSP passes from one to four, with and without Al₂O₃ powder. Microstructural observations were carried out by employing optical and scanning electron microscopy (SEM) of the cross sections both parallel and perpendicular to the tool traverse direction. Mechanical properties include microhardness and wear resistance, were evaluated in detail. The results show that the increasing in number of FSP passes causes a more uniform in distribution of nano-sized alumina particles. The microhardness of the surface improves by three times as compared to that of the as-received Al alloy. A significant improvement in wear resistance in the nano-composite surfaced Al is observed as compared to the as-received Al.     

Photocatalytic activity of pulsed laser deposited TiO2 thin films in N2, O2 and CH4

We report on pulsed laser deposition of TiO₂ films on glass substrates in oxygen, methane, nitrogen and mixture of oxygen and nitrogen atmosphere. The nitrogen incorporation into TiO₂ lattice was successfully achieved, as demonstrated by optical absorption and XPS measurements. The absorption edge of the N-doped TiO₂ films was red-shifted up to ∼ 480 nm from 360 nm in case of undoped ones.The photocatalytic activity of TiO₂ films was investigated during toxic Cr(VI) ions photoreduction to Cr(III) state in aqueous media under irradiation with visible and UV light. Under visible light irradiation, TiO₂ films deposited in nitrogen atmosphere showed the highest photocatalytic activity, whereas by UV light exposure the best results were obtained for the TiO₂ structures deposited in pure methane and oxygen atmosphere.     

Role of A2 and A50 process on the oxide dispersion strengthened ferritic alloy fabricated by mechanical alloying

This study has investigated the effects of adding occasion of Stearic Acid (SA) on the characteristics of powder and properties of bulk with nominal composition of Fe–12Cr–2.5 W–0.4Ti–0.3Y₂O₃, which was fabricated by mechanical alloying and vacuum sintering. SA was milling with the powder mixture with 50 h (added before milling, A₅₀) or 2 h (added after 48 h milling, A₂). The resulted showed: SA could inhibit the agglomeration and retard the alloying process. Powders through A₂ process achieved alloying with high powder yield, while the A₅₀ powders presented alloying extent, and the yield of A₀ powder presented low powder yield. SA added in A₅₀ was almost dissolved into the matrix for the long milling duration, but SA added in A₂ was mostly volatilized during heating. A₂ bulk alloy was of better strength for the finer, more uniform grain and second phase and higher density than A₅₀ bulk.     

Influence of modulation ratio on the structure and mechanical properties of TiB2/TiAlN multilayered coatings

TiB₂/TiAlN multilayered coatings with various modulation ratios (t_TiB2:t_TiAlN) were grown using radio-frequency magnetron sputtering at room temperature. Nanoindentation, tester for material surface properties, and XRD were used to investigate the influence of modulation ratio on microstructure and properties of the multilayers. All multilayers showed improved mechanical properties, compared with the average value of the monolithic TiB₂ and TiAlN coatings. The multilayer with modulation ratio of 5:2 displayed the highest hardness (36 GPa) and longest time to crack during wear. A marked layer structure with the strong mixture of TiAlN (111), AlN (111), and TiB₂ (001) textures with smaller grain sizes was responsible for the enhanced hardness.     

Modulating calcium phosphate formation using CO2 laser engineering of a polymeric material

The use of simulated body fluid (SBF) is widely used as a screening technique to assess the ability of materials to promote calcium phosphate formation. This paper details the use of CO₂ laser surface treatment of nylon® 6,6 to modulate calcium phosphate formation following immersion in SBF for 14 days. Through white light interferometry (WLI) it was determined that the laser surface processing gave rise to maximum Ra and Sa parameters of 1.3 and 4.4 μm, respectively. The use of X-ray photoelectron spectroscopy (XPS) enabled a maximum increase in surface oxygen content of 5.6%at. to be identified. The laser-induced surface modifications gave rise to a modulation in the wettability characteristics such that the contact angle, θ, decreased for the whole area processed samples, as expected, and increased for the patterned samples. The increase in θ can be attributed to a transition in wetting nature to a mixed-state wetting regime. It was seen for all samples that calcium phosphate formed on each surface following 14 days. The largest increase in mass, Δg, owed to calcium phosphate formation, was brought about by the whole area processed sample irradiated with a fluence of 51 J cm^− 2. No correlation between the calcium phosphate formation and the laser patterned surface properties was determined due to the likely affect of the mixed-state wetting regime. Strong correlations between θ, the surface energy parameters and the calcium phosphate formation for the whole area processed samples allow one to realize the potential for this surface treatment technique in predicting the bone forming ability of laser processed materials.