Crystallization and hardening of Zr-40 at.% Cu thin film metallic glass: Effects of isothermal annealing

Effects of isothermal annealing on structural relaxation, crystallization and mechanical behavior of Zr-40 at.% Cu thin film metallic glass (TFMG) are reported. Two annealing temperatures have been chosen in the supercooled liquid region (ΔT) and one below the glass transition temperature (T_g). During annealing the free volume decreased and nanocrystals nucleated into the matrix. Results show that the nanocrystalline CuZr₂ intermetallic phase precipitates in the glassy matrix with respect to the annealing temperature and duration. When annealed below T_g, the structural relaxation induces a slight improvement of the mechanical properties with a hardness and Young's modulus variation of about 2.5% and 9.0% compared with the as-deposited values. At higher temperatures, it is shown that hardness increases of about 5.5% and 25.0% after a heat treatment of 60 min at 350 °C and 380 °C, respectively. The elastic modulus follows a time dependent increase from ~ 100 GPa (as-deposited) up to ~ 105 GPa after a one-hour annealing at 350 °C and ~ 125 GPa at 380 °C, respectively.     

Mechanical properties of conventional and nanostructured plasma sprayed alumina coatings

The hardness and the elastic modulus measured by microindentation of three different types of plasma sprayed alumina coatings have been compared. Usually, such coatings present porosity and heterogeneity which affect the measurement of the mechanical properties. To take such effects into account along with the indentation size effect which is relevant to all hardness studies, the Proportional Specimen Resistance model is applied. The three alumina coatings show closely similar mechanical properties at indentation loads exceeding 1 N, i.e., macrohardness around 5.7 GPa, indentation size effect parameter around 5.5 MPa mm and elastic modulus around 160 GPa. For loads below 1 N, the extrapolated values of the macrohardness of crushed and agglomerated alumina coatings increased to 8.5 GPa, while the indentation size effect parameter has the same value, and the elastic modulus increased to 320 GPa. However, no significant change in the measured values of hardness and the elastic modulus of the nanostructured alumina coating has been observed. This result is attributed to porosity and the bimodal microstructure of the nanostructured coating where a semimolten phase coexists along with the fully molten phases.     

Effect of TiB2 content on the characteristics of spark plasma sintered Ti–TiBw composites

Spark plasma sintering (SPS) was employed to fabricate monolithic titanium and in-situ formed TiB whisker (TiB_w) reinforced titanium matrix composites (TMCs) by adding different amounts of TiB₂ as boron source. The sintering process was completed at 1050 °C for 5 min under 50 MPa. The influences of TiB₂ content (0.6–9.6 wt. %) on microstructural evolution and mechanical properties of TMCs were investigated. Thermodynamics, XRD analysis and microstructural investigations confirmed the in-situ formation of TiB_w in the composite samples. However, some semi-reacted TiB₂ phases, surrounded by TiB coronas, were remained in the microstructure due to the unfinished chemical reaction between the components during a short-time sintering process. The results showed that all samples were appropriately densified by SPS process into the almost dense parts with relative density no less than 97.5%. While bending strength decreased and hardness increased with increasing TiB₂ content, the sample with 4.8 wt. % TiB₂ had the maximum tensile strength. Fractographical assessments showed that the addition of TiB₂ hindered the grain growth of titanium matrix. With increasing TiB₂ content, fracture mode changed from a multiple pattern to a predominantly transgranular and brittle state.     

In-situ synthesis of TiC/Fe alloy composites with high strength and hardness by reactive sintering

Fe alloy composites reinforced with in-situ titanium carbide(Ti C) particles were fabricated by reactive sintering using different reactant C/Ti ratios of 0.8,0.9,1 and 1.1 to investigate the microstructure and mechanical properties of in-situ Ti C/Fe alloy composites.The microstructure showed that the in-situ synthesized Ti C particles were spherical with a size of 1–3 μm,irrespective of C/Ti ratio.The stoichiometry of in-situ Ti C increased from 0.85 to 0.88 with increasing C/Ti ratio from 0.8 to 0.9,but remained almost unchanged for C/Ti ratios between 0.9 and 1.1 due to the same driving force for carbon diffusion in Ti Cxat the common sintering temperature.The in-situ Ti C/Fe alloy composite with C/Ti = 0.9 showed improved mechanical properties compared with other C/Ti ratios because the presence of excess carbon(C/Ti = 1 and 1.1) resulted in unreacted carbon within the Fe alloy matrix,while insufficient carbon(C/Ti = 0.8)caused the depletion of carbon from the Fe alloy matrix,leading to a significant decrease in hardness.This study presents that the maximized hardness and superior strength of in-situ Ti C/Fe alloy composites can be achieved by microstructure control and stoichiometric analysis of the in-situ synthesized Ti C particles,while maintaining the ductility of the composites,compared to those of the unreinforced Fe alloy.Therefore,we anticipate that the in-situ synthesized Ti C/Fe alloy composites with enhanced mechanical properties have great potential in cutting tool,mold and roller material applications.     

Microstructure and mechanical properties of hot extruded 6016 aluminum alloy/graphite composites

The incorporation of graphite particles into AA6016 aluminum alloy matrix to fabricate metal/ceramic composites is still a great challenge and various parameters should be considered. In this study, dense AA6016 aluminum alloy/(0-20 wt%) graphite composites have successfully been fabricated by powder metallurgy process. At first, the mixed aluminum and graphite powders were cold compacted at 200 MPa and then sintered at 500 ℃ for 1 h followed by hot extrusion at 450 ℃. The influence of ceramic phases(free graphite and in-situ formed carbides) on microstructure, physical and mechanical properties of the produced composites were finally investigated. The results show that the fabricated composites have a relative density of over 98%. SEM observations indicate that the graphite has a good dispersion in the alloy matrix even at high graphite content. Hardness of all the produced composites was higher than that of aluminum alloy matrix. No cracks were observed at strain less than 23% for all hot extruded materials.Compressive strength, reduction in height, ultimate tensile stress, fracture stress, yield stress, and fracture strain of all Al/graphite composites were determined by high precision second order equations. Both compressive and ultimate tensile strengths have been correlated to microstructure constituents with focusing on the in-situ formed ceramic phases, silicon carbide(SiC) and aluminum carbide(Al_4 C_3). The ductile fracture mode of the produced composites became less dominant with increasing free graphite content and in-situ formed carbides. Wear resistance of Al/graphite composites was increased with increasing graphite content. Aluminum/20 wt% graphite composite exhibited superior wear resistance over that of AA6016 aluminum alloy.     

Effect of plasma CVD operating temperature on nanomechanical properties of TiC nanostructured coating investigated by atomic force microscopy

The structure, composition, and mechanical properties of nanostructured titanium carbide (TiC) coatings deposited on H₁₁ hot-working tool steel by pulsed-DC plasma assisted chemical vapor deposition at three different temperatures are investigated. Nanoindentation and nanoscratch tests are carried out by atomic force microscopy to determine the mechanical properties such as hardness, elastic modulus, surface roughness, and friction coefficient. The nanostructured TiC coatings prepared at 490 °C exhibit lower friction coefficient (0.23) than the ones deposited at 470 and 510 °C. Increasing the deposition temperature reduces the Young's modulus and hardness. The overall superior mechanical properties such as higher hardness and lower friction coefficient render the coatings deposited at 490 °C suitable for wear resistant applications.     

Y2O3–Nd2O3 double stabilized ZrO2–TiCN nanocomposites

Yttria-neodymia double stabilized ZrO₂-based nanocomposites with 40 vol% electrical conductive TiCN were fully densified by means of pulsed electric current sintering (PECS) in the 1400–1500 °C range. The Y₂O₃ stabilizer content was fixed at 1 mol% whereas the Nd₂O₃ co-stabilizer content was varied between 0.75 and 2 mol% in order to optimise the mechanical properties. The mechanical (Vickers hardness, fracture toughness and bending strength), electrical (electrical resistivity) and microstructural properties were investigated and the hydrothermal stability in steam at 200 °C was assessed.The nanocomposites with 1–1.75 mol% Nd₂O₃, PECS at 1400 or 1450 °C, have an excellent fracture toughness of 8 MPa m^1/2, although the grain size of both ZrO₂ and TiCN phases after densification is in the 100 ± 30 nm range. Moreover, the composites combine a hardness of about 13 GPa, a bending strength of 1.1–1.3 GPa with a low electrical resistivity (1.6–2.2 × 10^?5 Ω m) allowing electrical discharge machining. The hydrothermal stability of the double stabilizer nanocomposites was higher than for yttria-stabilized ZrO₂-based composites with the same overall stabilizer content.     

Influence of ZnO/graphene nanolaminate periodicity on their structural and mechanical properties

Structural, electronic and mechanical properties of ZnO/Graphene (ZnO/G) nanolaminates fabricated by low temperature atomic layer deposition (ALD) and chemical vapor deposition (CVD) were investigated. We performed scanning and transmission electron microscopy (SEM/TEM), X-ray diffraction (XRD), electron energy loss spectroscopy (EELS), Raman spectroscopy, X-Ray photoelectron spectroscopy (XPS) and nanoindentation to characterize the ZnO/G nanolaminates. The main structural and mechanical parameters of ZnO/G nanolaminates were calculated. The obtained results were analyzed and interpreted taking into account mechanical interaction and charge effects occurring at the G-ZnO interface. The influence of graphene sublayers number on the mechanical behavior of the ZnO/G nanolaminates was studied. By reducing the bilayer thickness, the mechanical parameters of the films can be tuned (Young’s modulus 100–200 GPa, hardness 3–9 GPa). The softer response of the multilayers as compared to the single layers of ZnO and graphene was attributed to the structural changes in the ZnO layer and the interfaces. This study shows the mechanical behavior of ZnO/G nanolaminates and their influence on the development of novel electro-optical devices based on these structures.     

Effect of cooling rate on microstructure,microsegregation and mechanical properties of cast Ni-based superalloy K417G

The effects of different solidification rates after pouring on the microstructures,microsegregation and mechanical properties of cast superalloy K417 G were investigated.Scheil-model was applied to calculate the temperature range of solidification.The casting mould with different casting runners was designed to obtain three different cooling rates.The microstructures were observed and the microsegregation was investigated.Also,high temperature tensile test was performed at 900?C and stress rupture test was performed at 950?C with the stress of 235 MPa.The results showed that the secondary dendrite arm spacing,microsegregation,the size and volume fraction of γ'phase and the size of γ/γ'eutectic increased with decreasing cooling rate,but the volume fraction of γ/γ' eutectic decreased.In the cooling rate range of 1.42?C s~(-1)–0.84?C s~(-1),the cast micro-porosities and carbides varied little,while the volume fraction and size of phase and γ/γ' eutectic played a decisive role on mechanical properties.The specimen with the slowest cooling rate of 0.84?C s~(-1) showed the best comprehensive mechanical properties.     

Fracture toughness determination and microstructure investigation of a B4C–NanoTiB2 composite with various volume percent of Fe and Ni additives

Boron carbide (B₄C) has wide application in manufacturing of abrasives and cutting tools, due to its unique features such as high hardness, good wear resistance, low specific weight and chemical stability. An additive reinforcing phase and sintering aids are used to improve its sinterability. In the present paper, a B₄C composite with 10 vol.% of titanium diboride nanoparticles (TiB₂) and a 0, 1.5 and 2.5 vol.% iron or nickel metallic additive, respectively, was mixed in an isopropanol environment containing tungsten carbide pellets. After drying, the obtained mixture was formed by cold pressing. The obtained parts were sintered at 2400 °C. The effect of adding metallic sintering aids on the mechanical properties and microstructure of the composite was investigated and fracture toughness values were evaluated by indentation test method. Addition of Fe and Ni improved values for density, hardness, Young’s modulus and fracture toughness, with Ni addition increasing the values considerably. Scanning electron microscope (SEM) images of the microstructure of the specimens showed the arrangement posture of the additives and confirmed the results obtained. Additionally, the FeB and Ni₃B blades formation were observed from the images.     

Laser-assisted synthesis of Ti–Mo alloys for biomedical applications

This paper presents the results of a laser-based combinatorial investigation of the Ti–Mo system, aiming at finding alloys with promising properties for orthopedic applications. Variable powder feed rate laser cladding was applied to synthesize Ti–xMo alloys with composition continuously varying in the range of 4–19 wt.% Mo. Screening was performed on the basis of the alloys' mechanical properties, in particular hardness and Young's modulus, measured by microindentation tests. Microstructural analysis showed that alloys with Mo content between 4 and 8 wt.% are composed of acicular martensite and retained β-phase, the proportion of the later phase increasing with increasing Mo content. Alloys with Mo content of 10 wt.% and higher consist entirely of β phase. All the alloys present a Mo segregation pattern indicating that solidification occurred with a cellular solid–liquid interface. Though β-phase alloys present lower values of Young's modulus and hardness than α′- or α″- containing alloys, minimum values of Young's modulus (75 GPa) and hardness (240 VHN) were achieved for the Ti–13 wt.% Mo alloy.     

Influence of the impact sintering temperature on the structure and properties of samples from the different iron powders

The studies of the consolidation, structure and mechanical properties of samples from two types of iron powder are carried out. The coarse and less pure PZH3M2 as well as fine and purer DIAFE5000 powders were used. The samples are obtained by means of impact sintering method in the temperatures range of 500–1100 °C. The impact energy was 1200 J/cm³, and the initial deformation velocity - 6.5 m/s. Samples are obtained in the form of disks with a diameter of 25–27 mm and 9–10 mm high. For carrying out different mechanical tests the bars were cut out from disks. The tensile, compression, three-point bend of notched samples tests were carried out, as well as the Brinell hardness was measured after the corresponding processing of the bars. The characteristics of strength and plasticity of samples depending on the impact sintering temperature are determined. The polished surface of different samples and the fracture surface are investigated. It is established that the high density of samples is reached at a temperature of 600 and 700 °C respectively for fine and coarse powders. The samples obtained at these impact sintering temperatures possess rather low electrical resistivity, high strength, hardness, but the lowered plasticity. Namely, the samples from the PZH3M2 and DIAFE5000 powders sintered at the temperature of 700 °C have respectively: ultimate tensile strength - 406 and 336 MPa, yield stress - 353 and 190 MPa, contraction ratio - 26 and 78%, limit stress (at the fracture) - 501 and 933 MPa, the maximum crack tip stress – 738 and 876 MPa, the fracture energy at a bend of the notched samples - 4.8 and 51.2 J/cm³ and also Brinell hardness - 1467 and 847 MPa. The increase of the samples impact sintering temperature leads to grain growth, decrease of the samples strength and increase of their plasticity. At the same time the structure of samples from the DIAFE5000 powder is more fine-grained than at samples from the PZH3M2 powder.     

New ductile laminate structure of Ti-alloy/Ti-based metallic glass composite with high specific strength

Bulk laminate structure of Ti-alloy/Ti-based metallic glass composite(MGC) was prepared by melting a preform of alternate stack-up foils in the high vacuum atmosphere. The composite demonstrates a good combination of yield strength(~1618 MPa), plasticity(~4.3%) and specific fracture strength(384 × 10~3 Nmkg~(-1)) in compression. The maintained yield strength results from the unique microstructure composed of the Ti layer, the solution layer with gradient structure and the MGC layer. Such a multilayer structure effectively inhibits the propagation of shear band, leading to the enhanced plasticity. Those extraordinary properities suggest that combining ductile lamella with brittle metallic glass(MG) by such a lay-up method can be an effective way to improve mechanical properties of MG.     

Microstructure characterization,mechanical properties,compressibility and sintering behavior of Al-B4C nanocomposite powders

In the present work, Al-xB₄C nanocomposite (x = 0, 1, 2, 3, 4 and 5 in wt%, having the average B₄C size of 50 nm) were prepared using a high-energy ball mill. The milling times up to 16 h were applied. Then, the microstructural evolutions, mechanical properties, compressibility and sintering behavior of nanocomposites were investigated. The changes in powders morphology and microstructure during the milling process were characterized by laser diffraction particle size analyzer (LDA), SEM, XRD, EDS and TEM techniques. Compressibility and sintering behavior of milled powders compacted under different pressures (100–900 MPa) and at different sintering temperatures (500, 550 and 600 °C) were also studied. The pressing behavior of the nanocomposites was analyzed using linear compaction equations developed by Heckel, Panelli-Filho and Ge. The results showed the significant effects of B₄C amounts and sintering temperatures on the compressibility and sintering behavior of nanocomposites. The increase in the B₄C amount led to a decrease in both the compressibility rate and the sinterability of specimens. The maximum compression strength of 265 MPa and Vickers hardness of 165 VHN were obtained for Al-5 wt.% B₄C nanocomposite milled for 16 h followed by sintering at 600 °C.     

Nanomechanical properties of hydroxyapatite (HAP) with DAB dendrimers (poly-propylene imine) coatings onto titanium surfaces

Coatings of hydroxyapatite (HAP) nanorods onto titanium surfaces were synthesized with the aim to improve coatings’ mechanical properties and adhesion to the substrate. The coatings are consisting of HAP nanorods synthesized in the presence of a cationic fourth generation diaminobutane poly(propylene imine) dendrimer (DAB) bearing 32 amine end groups employing varying calcium: dendrimer ratios and varying hydrothermal treatments. The quality, surface morphology and structure of the coatings were characterized with X-ray diffraction, thermogravimetric analysis, scanning electron microscopy and energy dispersive microanalysis. Wear resistance and adhesion properties of the coatings onto titanium substrates were studied through nanoindentation analysis. The experimental conditions, namely the calcium: dendrimer molar ratio and the hydrothermal treatment temperature were carefully selected; thus, it was possible to produce coatings of high hardness and elastic modulus values (ranging between 1–4.5 GPa and 40–150 GPa, respectively) and/or high wear resistance and plastic deformation values.     

Cell-wall hardness and Young's modulus of melamine-modified spruce wood by nano-indentation

Samples of spruce wood were infiltrated with a melamine–formaldehyde resin. After curing of the resin, a melamine concentration of 24% (v/v) was measured in the secondary cell walls of melamine treated wood. Nano-indentation tests revealed an average Young's modulus of 16.1 GPa and a hardness of 0.24 GPa for untreated secondary cell walls. In the melamine treated cell walls, an increase in the Young's modulus of 33% to 21.4 GPa was observed. With 115%, i.e. 0.52 GPa, the increase in longitudinal hardness due to melamine–formaldehyde treatment was even more pronounced. This proves clearly that melamine treatment of wood improves mechanical properties of cell walls. Thus, treatment of wood with melamine–formaldehyde resin shows a considerable potential to improve mechanical properties, as desired for applications where large stresses normal to grain arise.     

Microstructural changes and mechanical properties of Incoloy 800 after 15 years service

Microstructure and mechanical properties of Incoloy 800 superalloy before (as-received) and after 15 years service exposure were evaluated. The metallurgical variations such as formation and growth of the secondary precipitates, phase transformation of titanium carbide to Cr₂₃C₆ + Ni₁₆Ti₆Si₇ and decomposition of primary carbides were characterized during the long-term service of Alloy 800. It was shown that some of chromium and iron elements were moved from solid solution to the carbides during the service exposure. It was found that due to the formation of precipitates during service, the strength and hardness of Alloy 800 were improved, while the ductility and toughness were reduced.     

Preparation and properties of porous Ti–10Mo alloy by selective laser sintering

In this study, porous Ti–10Mo alloy was prepared from a mixture of titanium, molybdenum and epoxy resin powders by selective laser sintering preforming, debinding and sintering at 1200 °C under a pure argon atmosphere. The influence of sintering process on the porous, microstructural and mechanical properties of the porous alloy was discussed. The results indicate that the pore characteristic parameters and mechanical properties mainly depend on the holding time at 1200 °C, except that the maximum strain keeps at about 45%. The matrix microstructure is dominated by α phase with a small quantity of β phase at room temperature. As the holding time lengthens from 2 to 6 h, the average pore size and the porosity decrease from 180 to 50 μm and from 70 to 40%, respectively. Meanwhile, the Young's modulus and the compressive yield strength increase in the ranges of 10–20 GPa and 180–260 MPa, respectively. Both the porous structure and the mechanical properties of the porous Ti–10Mo alloy can be adjusted to match with those of natural bone.     

Tensile,creep behavior and microstructure evolution of an as-cast Ni-based K417G polycrystalline superalloy

The Ni-based K417G superalloy is extensively applied as aeroengine components for its low cost and good mid-temperature (600–900 °C) properties. Since used in as-cast state, the comprehensive understanding on its mechanical properties and microstructure evolution is necessary. In the present research, the tensile, creep behavior and microstructure evolution of the as-cast K417G superalloy under different conditions were investigated. The results exhibit that tensile cracks tend to initiate at MC carbide and γ/γ′ eutectic structure and then propagate along grain boundary. As the temperature for tensile tests increases from 21 °C to 700 °C, the yield strength and ultimate tensile strength of K417G superalloy decreases slightly, while the elongation to failure decreases greatly because of the intermediate temperature embrittlement. When the temperature rises to 900 °C, the yield strength and ultimate tensile strength would decrease significantly. The creep deformation mechanism varies under different testing conditions. At 760 °C/645 MPa, the creep cracks initiate at MC carbides and γ/γ′ eutectic structures, and propagate transgranularly. While at 900 °C/315 MPa and 950 °C/235 MPa, the creep cracks initiate at grain boundary and propagate intergranularly. As the creep condition changes from 760 °C/645 MPa to 900 °C/315 MPa and 950 °C/235 MPa, the γ′ phase starts to raft, which reduces the creep deformation resistance and increases the steady-state deformation rate.     

Correlation between anionic substitution and structural properties in AlCr(OxN1−x) coatings deposited by lateral rotating cathode arc PVD

The influence of oxygen content on the properties of cathodic arc-deposited AlCr(O_xN_1?x) coatings has been studied. All samples were prepared in a nitrogen-rich mixture of N₂ and O₂ at 550 °C using lateral rotating arc cathodes (LARC) technology together with a pulsed bias voltage. The obtained coatings were characterized by various techniques including XRD, EPMA, TEM, pin-on-disk wear tests and nanoindentation. The results obtained allow to classify the coatings into three groups with respect to their microstructure, mechanical properties and oxygen content, x. For the first group of samples with x ≤ 0.6, single-phase films of (Al,Cr)O_xN_1-x with fcc lattice were obtained, with well-developed columnar structure and a hardness of 30 to 33 GPa. In the second group, a diffuse columnar structure was observed while the fcc lattice was still present despite the large proportion of oxygen, 0.6 < x ≤ 0.97, and the observed hardness decreased to 25 GPa. No amorphous phase was detected in this group as confirmed by TEM. The simulation of XRD patterns of nitride lattices with oxygen incorporation allowed to suggest the formation of cation vacancies in the structure of the investigated oxynitride coatings. The third group is formed by coatings with x > 0.97, where a well-crystalline α-(Al,Cr)₂O₃ corundum phase was observed and the hardness increased again to 28 GPa. Our results indicate that the second group of coatings is metastable and after heat treatment transforms to a composite of cubic oxynitride and corundum oxide. Both friction and wear of samples from the entire investigated compositional range were studied at room temperature and 600 °C. The low wear rates observed for the oxynitride coatings underline their potential for use in turning and milling applications.