Nanoscale Crystallization in the Amorphous Alloy Fe79P14.2Si4.4Mn2.2V0.2 upon Pulsed Photon Annealing

The effect of pulsed photon annealing with energy densities from 1.4 to 42 J/cm² for various lengths of time on the structure of the amorphous alloy Fe₇₉P_14.2Si_4.4Mn_2.2V_0.2 was studied by x-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. The results demonstrate that short-term irradiation with low energy densities leads to surface relaxation of the amorphous alloy, increases the strength of the surface layer, and reduces the internal-friction peak. Longer term photon annealing leads to crystallization of the alloy throughout the sample thickness.     

Ion beam nitriding of titanium and titanium alloy

Titanium and Ti8A/1Mo1V alloy have been nitrided with an ion beam source of nitrogen or agon and nitrogen, at a total pressure of 2?10×10^?4 torr. The treated surface has been characterized by surface profilometry, X-ray diffractometry, Auger Electron Spectroscopy (AES), and microhardness measurements. It was found that tetragonal Ti₂N phase forms in pure titanium and Ti8A/2Mo1V alloy with traces of AIN in the alloy. Two opposite processes were found to compete during the ion beam nitriding: (a) formation of nitrides in the surface layers; (b) sputtering of the nitrided layers by the ion beam. The highest surface hardness, of about 500 kg mm^?2 in titanium and 800 kg mm^?2 in Ti8A/1Mo1V, was obtained by nitriding with an ion beam of pure nitrogen at 4.2×10^?4 torr, at beam voltage of 1000 V.     

Effect of Al2O3 and Fe3Al on the phase formation and mechanical properties of β-sialon

The paper evaluated the mechanical properties of β-sialon composites prepared by hot-pressing sintering at 1600 °C in N₂ atmosphere using α-Si₃N₄, Al₂O₃, Y₂O₃ and Fe₃Al as raw materials. The influence of Al₂O₃ and Fe₃Al content on flexure strength, fracture toughness, hardness, and relative density was investigated. And phase formation and morphology of the composites were characterized by X-ray diffraction and electron microscopy. The experimental results indicate that the raw material Fe₃Al reacts with α-Si₃N₄ to form silicides at elevated temperature, and supplies more liquid phase to assist densification. Besides, the variation of flexure strength, fracture toughness and hardness is mainly consistent, and also in good agreement with the relative density measurements. The values all increase firstly, and then decrease when the Al₂O₃ content increases. Scanning electron microscopy illustrates that the metal particles act to inhibit the crack propagation.     

Herstellung massiver metallischer Gläser aus kristallinen Gefügen durch lokales kleinvolumiges Umschmelzen

Metallic glasses, or the so‐called bulk metallic glasses (BMGs), have peculiar properties such as extreme strengths and hardness while their specific ferromagnetic properties can be controlled accurately by the alloy content which is due to their amorphous structure. This special properties combination makes them interesting for research and technology. In the current research work, the development of a novel method for the creation of amorphous structure via locally limited re‐melting of the crystalline Fe‐based pre‐alloys is presented. Two alloys, namely Fe₇₆Si₉B₁₀P₅ and Fe₄₃Co₇Cr₁₅Mo₁₄C₁₅B₆ (at.‐%), are produced by melting and slow solidification. The solidified dendritic, crystallographic bulk afterwards is locally heat treated by electron beam welding. Here, a high‐energy electron beam is focused onto the crystalline surface of the pre‐alloy, so that the material is melted rapidly at the surface for a short time and then re‐solidified very fast by self‐quenching. By this process technique both the surface and a relative big volume of the material is glazed. For the evaluation of the amorphous phase scanning electron microscopy coupled with energy dispersive X‐ray analysis (SEM/EDX) and high‐resolution electron diffraction based on transmission electron microscopy (HRTEM) were used. These methods are able to show the lack of structural order of the atoms and by that amorphous structures were evaluated [1].     

Correlation between the composition, structure and properties of dual ion beam deposited SiNx films

Silicon nitride (SiN_x) films were prepared by dual ion beam deposition at room temperature. An assisted N₂⁺ ion beam (current I_b=0-45 mA) was directed to bombard the substrate surface to control the N content x, which saturated at x≈1.36 when I_b?25 mA. The presence of SiN bonds was indicated by the appearance of a Si 2p photoelectron peak at 101.9 eV and an infrared absorption peak at 850 cm⁻¹. As x increases from 0 to 1.36, the hardness, elastic modulus and compressive stress increase from 12.2 to 21.5 GPa, 191 to 256 GPa and 0.52 to 1.4 GPa and the friction coefficient against stainless steel ball decreases from 0.65 to 0.37. The optical band gap increases remarkably with a concomitant drop in electrical conductivity (σ_RT) by more than 10⁷ times. Ion bombardment induces defects and trap states in the mid-gap, such that the transport mechanism is dominated by hopping of charge carriers through the trap states. Consequently, the activation energy of electrical conductivity is much lower than the optical band gap.     

Hardness improvement of surface alloyed materials fabricated with Fe based metamorphic powders by high energy electron beam irradiation

Abstract

In the present study, surface alloyed materials were fabricated with Fe based metamorphic powders by the high energy electron beam irradiation. A surface alloyed layer was fabricated by depositing metamorphic powders on a carbon steel substrate and by irradiating with high energy electron beam. On top of this surface alloyed layer, metamorphic powders were deposited once again and irradiated with electron beam to fabricate a two layered surface alloyed material. In the surface alloyed layers, 53–64 vol.-%Cr_1·65Fe_0·35B_0·96 borides were densely precipitated in the martensitic matrix. A large amount of hard borides improved the hardness of the surface alloyed layers 2–3 times greater than that of the substrate. In addition, they showed high hardness of ～500 VHN even at 450°C, because borides were thermally stable at high temperatures. These results suggested potentials of the fabricated surface alloyed materials for applications requiring good wear and thermal resistance.     

Synthesizing higher nitride of molybdenum (Mo) and iron (Fe) in ammonia (NH3) gas stream under irradiation of concentrated solar beam in a solar furnace

Flowing gaseous ammonia NH₃ with suppressed extent of dissociation (un‐cracked NH₃) is acknowledged to function as a powerful nitriding medium to realize formation of metal nitride MN_x with considerably high N/M ratio x that cannot be achieved through reaction of M with N₂ gas. For example, mono‐nitride δ‐MoN of Mo and ε‐FeN_x phase of Fe with x = 0.33 ? 0.50 (i. e. hypo‐stoichiometric sub‐nitride ε‐Fe₂N) were reported to be difficult to prepare in N₂ gas environment even at elevated pressure but might be synthesized in flowing NH₃ gas at normal pressure when reaction temperature and NH₃ gas flow rate were set adequately. In the present work, nitriding experiments for Mo and Fe were carried out in flowing NH₃ gas under irradiation with concentrated solar beam. The acquired experimental evidences demonstrated that temperature range for formation of δ‐MoN was somewhat extended in flowing NH₃ gas under heating with concentrated solar beam compared with that under heating in conventional laboratory or industrial electric furnace. On the other hand, no such merit of extending temperature range for formation of ε‐Fe₂N in flowing NH₃ gas was detected in the present work under heating with concentrated solar beam.     

First-principles study of ZrC x N1−x alloys with electron concentration modulation

The structural and mechanical properties of the ZrC _x N_1?x alloys with electron concentration modulation were systematically investigated by using the pseudopotential plane wave method within the generalized gradient approximation. The obtained equilibrium structure parameters and mechanical properties are in good agreement with the available experimental and other theoretical results. In addition, the theoretical Vickers hardness of ZrC _x N_1?x was calculated with the empirical formula. With an increase in carbon content in this alloys the hardness increases as carbon content up to 70 % then decreases a little, which has the same hardness change trend comparing with that of TiC _x N_1?x . Also, it was found that ZrC_0.7N_0.3 alloy with a valence-electron concentration of 8.3 per unit cell possesses the greatest hardness among the whole composition range. Furthermore, the analysis of electronic properties revealed the metallic character of ZrC_0.7N_0.3 alloy. The thermodynamic stability of the designed alloy was also estimated by the calculated mixing enthalpy.     

Surface electron beam melting and alloying of tool steels

Abstract

Surface melting and alloying of D3 steel using an electron beam has been carried out to improve its surface microstructure and properties. The solution of primary carbides, together with rapid solidification and subsequent cooling, enhance the solubility of alloying elements in the γ Fe phase and thus influence the behaviour of the steel on subsequent tempering. The surface melted zone consists of dendrites without primary carbides, which is also the case for samples alloyed with WC, SiC, or Al₂O₃. When alloyed with TiC or TiB₂, the materials contain TiC or TiB₂ primary phase respectively in addition to the iron rich dendrites. Some unmelted TiB₂ particles are also present. On tempering, both electron beam melting and alloying change the secondary hardening characteristics, increasing the peak hardness and the peak hardness temperature.

MST/1194     

Phase formation in selected surface-roughened plasma-nitrided 304 austenite stainless steel

Abstract

Direct current (DC) glow discharge plasma nitriding was carried out on three selected surface-roughened AISI 304 stainless steel samples at 833 K under 4 mbar pressures for 24 h in the presence of N₂:H₂ gas mixtures of 50 : 50 ratios. After plasma nitriding, the phase formation, case depth, surface roughness, and microhardness of a plasma-nitrided layer were evaluated by glancing angle x-ray diffractogram, optical microscope, stylus profilometer, and Vickers microhardness tester techniques. The case depth, surface hardness, and phase formation variations were observed with a variation in initial surface roughness. The diffraction patterns of the plasma-nitrided samples showed the modified intensities of the α and γ phases along with those of the CrN, Fe₄N, and Fe₃N phases. Hardness and case depth variations were observed with a variation in surface roughness. A maximum hardness of 1058 Hv and a case depth of 95 μm were achieved in least surface-roughened samples.     

Precipitation hardening in Al-Zn-Mg-Al2O3(p) composite

The precipitation hardening of a Al-Zn-Mg-Al₂O₃(p) composite is explored. It is found that the peak hardness achieved is almost double that of precipitation hardening of Al-Zn-Mg alloy or dispersion strengthening of Al-Zn-Mg with 5% Al₂O₃(p). Toughness is marginally improved and tensile strength is one and half times that of precipitation hardened Al-Zn-Mg alloys. The ageing time for peak hardness is reduced due to acceleration of formation of precipitate.     

Phase formation in selected surface-roughened plasma-nitrided 304 austenite stainless steel

Direct current (DC) glow discharge plasma nitriding was carried out on three selected surface-roughened AISI 304 stainless steel samples at 833 K under 4 mbar pressures for 24 h in the presence of N₂:H₂ gas mixtures of 50 : 50 ratios. After plasma nitriding, the phase formation, case depth, surface roughness, and microhardness of a plasma-nitrided layer were evaluated by glancing angle x-ray diffractogram, optical microscope, stylus profilometer, and Vickers microhardness tester techniques. The case depth, surface hardness, and phase formation variations were observed with a variation in initial surface roughness. The diffraction patterns of the plasma-nitrided samples showed the modified intensities of the α and γ phases along with those of the CrN, Fe₄N, and Fe₃N phases. Hardness and case depth variations were observed with a variation in surface roughness. A maximum hardness of 1058 Hv and a case depth of 95 μm were achieved in least surface-roughened samples.     

Microstructure,mechanical and erosion wear analysis of post heat treated iron alloy based coating with varying chromium

The present work focuses on the effect of annealing heat treatment on the microstructure, mechanical and erosion properties of iron alloy based coatings with varying chromium content. High velocity oxygen fuel coating method was used to deposit the coating over the substrate material 316 L stainless steel. The study was done in terms of microstructural analysis using x-ray diffractometer, surface and cross-sectional morphology using field emission scanning electron microscope, mechanical and erosion wear analysis. It was found that x-ray diffractometer indicated presence of less amount of titanium dioxide (TiO₂) and silicon dioxide (SiO₂) after heat treatment. However, the peaks of hardened phase of diironylidenetitanium (Fe₂Ti) and iron-chromium (Fe−Cr) was increased. Addition of chromium up to 10 wt. % improved the hardness and adhesion pull of strength by 16 % and 62 % respectively. On the other side heat treatment of iron alloy based coating having 10 wt. % chromium increased the hardness and adhesion pull off strength by 17.3 % and 35 % respectively. The erosion wear rate was also decreased with the annealing process. The study shows that the annealing process increases hardness and adhesion pull off strength but decreases porosity and erosion wear rate.     

Mechanical-contact-induced transformation from the amorphous to the partially crystalline state in metallic glass

Sliding friction and wear experiments and electron microscopy and diffraction studies were conducted to examine the metallurgical microstructure of a metallic glass surface strained in sliding contact. Friction and wear experiments were conducted with aluminium oxide spheres 3.2 and 6.4 mm in diameter sliding, in reciprocating motion, on a metallic foil with a composition of Fe₆₇Co₁₈B₁₄Si₁ at a sliding velocity of 1.5 mm s^-1 (frictional heating is negligible) with a load of 2.5 N at room temperature and in a laboratory air atmosphere.The results of the investigation indicate that the amorphous alloy (metallic glass) can be crystallized during mechanical contact. Crystallites with a size range of 10–150 nm are produced on the wear surface of the amorphous alloy. A diffused honeycomb-shaped structure formed by dark gray bands is also produced during sliding. Considerable plastic flow occurs on an amorphous alloy surface with sliding and the flow film of the alloy transfers to the aluminium oxide pin surface. Multiple slip bands due to shear deformation are observed on the side of the wear track. Two distinct types of wear debris were observed as a result of sliding: an alloy wear debris and/or powdery and whiskery oxide debris. The wear rate of Fe₆₇Co₁₈B₁₄Si₁ was 5 × 10^-9 mm³ N^-1.     

Microstructures of TiN and Ti2N deposits prepared by activated reactive evaporation

Titanium nitride has an important application as a coating on cutting tools to extend their lifetime. In this study various phases in the Ti-N system were deposited by the activated reactive evaporation process. The influence of process variables—evaporation rate, N₂ partial pressure and deposition temperature—on the phases present, their morphology and hardness, was studied using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. As the ratio of the evaporation rate of titanium to the partial pressure of N₂ decreases, the deposit changes from titanium to Ti₂N to TiN including two-phase mixtures. As the deposition temperature is increased the grain size increases markedly, from about 0.5 μm at 550 °C to 20 μm at 1000 °C, and the grain morphology changes from a faceted to a smooth topography. The hardness of the deposit is influenced primarily by the presence of the Ti₂N phase which produces the highest hardness levels.     

Surface characteristics of Ti-6Al-4V by SiC abrasive-mixed EDM with magnetic stirring

Ti-6Al-4V is widely used in aerospace, biomedical applications and in many corrosive environments. However, titanium alloy has low hardness and poor wear resistance. This paper introduces a machining method of SiC abrasive-mixed electrical discharge machining (EDM) with magnetic stirring. Structural features and chemical composition were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD). Micro-hardness distribution on the cross section was measured with an FM800 micro-hardness tester. The influence of pulse width and pulse peak current on the formation of the surface hardening layer is analyzed. The results show that a continuous strengthened layer was formed during the SiC abrasive-mixed EDM process. The hardness of the formed layer was significantly improved because of the formation of TiC and TiSi₂ phases on the machined surface. With the increase of pulse width, the thickness of the strengthened layer increases and the quality becomes better.     

Evaluation of the effects of plasma nitriding temperature and time on the characterisation of Ti 6Al 4V alloy

The effects of plasma nitriding (PN) temperature and time on the structural and tribological characterisation of Ti 6Al 4V alloy were investigated. PN processes under gas mixture of N₂/H₂ = 4 were performed at temperatures of 700, 750, 800 and 850 °C for duration of 2, 5 and 10 h. Cross section and surface characterisation were evaluated by means of SEM, AFM, XRD and microhardness test techniques. Dry wear tests were performed using a pin on disc machine. Mass loss and coefficient of friction were measured during the wear tests. Three distinguished structures including of a compound layer (constituted of δ-TiN and ɛ-Ti₂N), an aluminium-rich region and a diffusion zone (interstitial solid solution of nitrogen in titanium) were detected at the surface of plasma nitrided Ti 6Al 4V alloy. These structures increased surface hardness of Ti 6Al 4V alloy significantly and gradually distributed the hardness from the surface to the substrate. The "surface hardness", "surface roughness", "wear resistance" and "coefficient of friction" of the alloy were increased due to plasma nitriding process. Moreover, rising both process temperature and time led to increasing of "layers thicknesses", "surface hardness", "surface roughness", "dynamic load-ability" and "wear resistance" of Ti 6Al 4V alloy.     

Plasticity characterization of the modified layer produced by plasma nitrocarburizing of nanocrystallized 18Ni maraging steel

The plasma nitrocarburizing of nanocrystallized 18Ni maraging steel was performed at 460 °C for 4 h. The surface phase composition, cross-sectional microstructure and hardness profile of the nitrocarburized layer were investigated by the X-ray diffractometer (XRD), optical microscope (OM) and microhardness tester. Plasticity of the surface layer of original and nitrocarburized samples was analyzed by Taylor factor obtained by electron backscattering diffraction (EBSD) data and nanoindentation tests. The nitrocarburized surface is composed of α-Fe, Fe₄N and a small fraction of low nitrogen compound FeN_0.049. The surface and core hardness of nitrocarburized samples are 200% and 130% of that of the original one, respectively. The Taylor factors for different slip systems of α-Fe grains are all decreased after nitrocarburizing and Taylor factors for Fe₄N grains are lower than those of basal slip system of α-Fe grains. Plasticity factor η_p, i.e. the ratio of plastic deformation work to total deformation work dissipated during loading-unloading process, of the surface layer is reduced about 20% after nitrocarburizing. This suggests that plasticity and wear resistance of the surface layer could be decreased and improved after nitrocarburizing, respectively. The surface layer of the nitrocarburized sample also possesses certain plasticity because its plasticity factor η_p is more than 60%.     

Plasticity characterization of the modified layer produced by plasma nitrocarburizing of nanocrystallized 18Ni maraging steel

The plasma nitrocarburizing of nanocrystallized 18Ni maraging steel was performed at 460 °C for 4 h. The surface phase composition, cross-sectional microstructure and hardness profile of the nitrocarburized layer were investigated by the X-ray diffractometer (XRD), optical microscope (OM) and microhardness tester. Plasticity of the surface layer of original and nitrocarburized samples was analyzed by Taylor factor obtained by electron backscattering diffraction (EBSD) data and nanoindentation tests. The nitrocarburized surface is composed of α-Fe, Fe₄N and a small fraction of low nitrogen compound FeN_0.049. The surface and core hardness of nitrocarburized samples are 200% and 130% of that of the original one, respectively. The Taylor factors for different slip systems of α-Fe grains are all decreased after nitrocarburizing and Taylor factors for Fe₄N grains are lower than those of basal slip system of α-Fe grains. Plasticity factor η_p, i.e. the ratio of plastic deformation work to total deformation work dissipated during loading-unloading process, of the surface layer is reduced about 20% after nitrocarburizing. This suggests that plasticity and wear resistance of the surface layer could be decreased and improved after nitrocarburizing, respectively. The surface layer of the nitrocarburized sample also possesses certain plasticity because its plasticity factor η_p is more than 60%.     

Aging behavior of a CuCr2Fe2NiMn high-entropy alloy

The effect of aging treatment on the hardness and microstructure of a CuCr₂Fe₂NiMn high-entropy alloy is investigated. The results show that the alloy exhibits a good high-temperature age hardening phenomenon and temper resistance. The aged alloy can obtain a peak hardness of 450 HV at 800 °C. Softening anneal occurs at 1100 °C. Age hardening is mainly attributed to the precipitation hardening of the ρ phase and a more homogeneous microstructure, whereas the softening of the aged alloy may be related to the decomposition of the ρ phase and Cu-rich FCC1 and to the coarsening of the FCC2 phase in the interdendrite regions.