Rapid synthesis of Ti alloy with B addition by spark plasma sintering

The in situ TiB/Ti–4.0Fe–7.3Mo composites were fabricated by plasma spark sintering (SPS) technique using mechanical alloying of Ti, Fe65Mo and B powder. The effects of sintering temperature on densification of the composites and microstructure of the in situ synthesized TiB were investigated using scanning electron microscope (SEM) and transmission electron microscope (TEM). A dense composite was obtained after sintering at 1000 °C for 5 min. Under proper ball milling and SPS conditions in situ TiB reinforced Ti–4.0Fe–7.3Mo composites have been prepared. The in situ TiB showed a typical needle shape grow along [0 1 0] direction. The transverse cross-section of TiB grain is a hexagonal shape with the planes of (1 0 0), (1 0 1) and . The stacking faults in the (1 0 0) plane were observed in the TiB needles.     

Fracture behaviour of hybrid glass matrix composites: thermal ageing effects

The thermal aging of a glass matrix composite reinforced by short carbon fibres as well as by ZrO₂ particles (hybrid composite) was investigated at temperatures in the range 500–700 °C for exposure durations of 24 h in air. The mechanical properties of as-received and aged samples were evaluated at room temperature by using the three-point flexure chevron notch technique. The fracture toughness values of as-received specimens were in the range 2.6–6.4 MPa m^1/2. Fracture toughness was affected by the thermal aging conditions. For thermal aging at temperatures <700 °C, degradation of fibre–matrix interfaces occurred and therefore the apparent fracture toughness and flaw tolerant resistance decreased. For the most severe ageing conditions tested (700 °C/24 h), fracture toughness values dropped to 0.4 MPa m^1/2. Significant degradation of the material was detected for this aging condition, mainly characterised by porosity formation in the matrix as a result of softening of the glass and oxidation of the carbon fibres.     

Mechanical properties of 3D KD-I SiCf/SiC composites with engineered fibre-matrix interfaces

Three-dimensional (3D) silicon carbide (SiC) matrix composites reinforced with KD-I SiC fibres were fabricated by precursor impregnation and pyrolysis (PIP) process. The fibre-matrix interfaces were tailored by pre-coating the as-received KD-I SiC fibres with PyC layers of different thicknesses or a layer of SiC. Interfacial characteristics and their effects on the composite mechanical properties were evaluated. The results indicate that the composite reinforced with as-received fibre possessed an interfacial shear strength of 72.1 MPa while the composite reinforced with SiC layer coated fibres had a much higher interfacial shear strength of 135.2 MPa. However, both composites showed inferior flexural strength and fracture toughness. With optimised PyC coating thickness, the interface coating led to much improved mechanical properties, i.e. a flexural strength of 420.6 MPa was achieved when the interlayer thickness is 0.1 μm, and a fracture toughness of 23.1 MPa m^1/2 was obtained for the interlayer thickness of 0.53 μm. In addition, the composites prepared by the PIP process exhibited superior mechanical properties over the composites prepared by the chemical vapour infiltration and vapour silicon infiltration (CVI-VSI) process.     

Temperature dependence of fracture toughness of silica/epoxy composites: Related to microstructure of nano- and micro-particles packing

Temperature dependence of the fracture toughness of epoxy composites reinforced with nano- and micro-silica particles was evaluated. Epoxy composites containing varied composition ratios Φ_SP of spherical nano- and micro-silica particles, 240 nm and 1.56 μm, were prepared at a fixed volume fraction (V_P = 0.30). The thermo-viscoelasticity and fracture toughness of the composites and neat epoxy were measured at 143 K, 185 K, 228 K, 296 K, 363 K, and 399 K. Experimental results revealed that fracture toughness strongly depended on the microstructure of nano- and micro-particles bidispersion as well as its interactions with the matrix at all temperature, but depended on toughened matrix due to increase in mobility of matrix at the relaxation temperatures.     

Synthesis and mechanical properties of niobium aluminide-based composites

Niobium aluminide-based composites reinforced with in situ and externally added Al₂O₃ and TiC particulates were fabricated by hot-pressed sintering at 1400 °C. In particular, Nb₂Al–Al₂O₃–TiC in situ composites were successfully obtained from the raw powder mixtures of Nb60Al40 (in at.%)–TiO₂20C8 (in wt.%) by means of this process. The influences of ceramic particulates on the microstructures, flexural strength and fracture toughness were examined. The experimental results indicate that the presence of ceramic particulates yielded a remarkable improvement in both the strength and fracture toughness in comparison with previous results for monolithic niobium aluminide compounds.     

Fabrication of (TiB/Ti)-TiAl composites with a controlled laminated architecture and enhanced mechanical properties

The(TiB/Ti)-TiAl composites with a laminated structure composing of alternating TiB/Ti composite layers,α₂-Ti₃Al interfacial reaction layers of andγ-TiAl layers were successfully pre pared by spark plasma sintering of alternately stacked Tib₂/Ti powder layers and TiAl powder layers.And the influence of thickness ratio of Tib₂/Ti powder layers to TiAl powder layers on microstructure evolution and mechanical properties of the re sulting(TiB/Ti)-TiAl laminated composites were investigated systemically.The results showed that the thickening ofα₂-Ti₃Al layers which originated from the reaction of Ti and TiAl was significantly hindered by introducing Tib₂particles into starting Ti powders.As the thickness ratio of Tib₂/Ti powder layers to TiAl powder layers increased,the bending fracture strength and fracture toughness at room temperature of the final(TiB/Ti)-TiAl laminated composites were remarkably improved,especially for the(TiB/Ti)-TiAl composites prepared by Tib₂/Ti powder layers with thickness of 800μm and TiAl powder layers with thickness of 400μm,whose fracture toughness and bending strength were up to 51.2 MPa·m^1/2and 1456 MPa,respectively,293%and 108%higher than that of the monolithic TiAl alloys in the present work.This was attributed to the addition of high-performance network TiB/Ti composite layers.Moreover,it was noteworthy that the ultimate tensile strength at 700℃of(TiB/Ti)-TiAl composites fabricated by 400μm thick Tib₂/Ti powder layers and 400μm thick TiAl powder layers was as high as that at 550℃of network TiB/Ti composites.This means the service temperature of(TiB/Ti)-TiAl laminated composites was likely raised by 150℃,meanwhile a good combination of high strength and high toughness at ambient tempe rature could be maintained.Finally,the fracture mechanism of(TiB/Ti)-TiAl laminated composites was proposed.     

In situ synthesis mechanism and characterization of ZrB2–ZrC–SiC ultra high-temperature ceramics

The synthesis route, microstructure and properties of ZrB₂–ZrC–SiC composites prepared from a mixture of Zr–B₄C–Si powders by in situ reactive synthesis were investigated. The reactive path and synthesized mechanism of ZrB₂–ZrC–SiC composite were studied through series of pressureless heat treatments ranging from 800 °C to 1700 °C in argon. The in situ ZrB₂–ZrC–SiC composites were fabricated under different synthesis processing. The one with 88.4% relative density performed poorly in mechanical properties due to the occurring of self-propagating high-temperature synthesis (SHS). The fully dense ZrB₂–ZrC–SiC composite was obtained under the optimized synthesis processing without SHS reactions. Its Vickers hardness, flexural strength and fracture toughness were 20.22 ± 0.56 GPa, 526 ± 9 MPa and 6.70 ± 0.20 MPa m^1/2, respectively.     

Synthesis, structure refinement and characterization of tetrahydrated acid gadolinium diphosphate HGdP2O7·4H2O

Synthesis and single crystal structure are reported for a new gadolinium acid diphosphate tetrahydrate HGdP₂O₇·4H₂O. This salt crystallizes in the monoclinic system, space group P2₁/n, with the following unit-cell parameters: a = 6.6137(2) Å, b = 11.4954(4) Å, c = 11.377(4) Å, β = 87.53(2)° and Z = 4. Its crystal structure was refined to R = 0.0333 using 1783 reflections. The corresponding atomic arrangement can be described as an alternation of corrugated layers of monohydrogendiphosphate groups and GdO₈ polyhedra parallel to the () plane. The cohesion between the different diphosphoric groups is provided by strong hydrogen bonding involving the W4 water molecule.

IR and Raman spectra of HGdP₂O₇·4H₂O confirm the existence of the characteristic bands of diphosphate group in 980–700 cm⁻¹ area. The IR spectrum reveals also the characteristic bands of water molecules vibration (3600–3230 cm⁻¹) and acidic hydrogen ones (2340 cm⁻¹). TG and DTA investigations show that the dehydration of this salt occurs between 79 and 900 °C. It decomposes after dehydration into an amorphous phase. Gadolinium diphosphate Gd₄(P₂O₇)₃ was obtained by heating HGdP₂O₇·4H₂O in a static air furnace at 850 °C for 48 h.     

Effects of ZnO on piezoelectric properties of 0.01PMW–0.41PNN–0.35PT–0.23PZ ceramics

The microstructure and piezoelectric properties of the 0.01Pb(Mg_1/2W_1/2)O₃–0.41Pb(Ni_1/3Nb_2/3)O₃–0.35PbTiO₃–0.23PbZrO₃ + 0.1 and 0.3 wt.% Y₂O₃ + x ZnO ceramics were investigated. The crystal structure changed from psudocubic to tetragonal when ZnO added. The average grain size increased from 4 μm to 8 μm with the addition of ZnO by oxygen diffusion, even if the growth rate was low. When ZnO added until 0.5 wt.%, the , k_p and d₃₃ values of specimens were slightly increased regardless Y₂O₃ contents. The curie point of PMW–PNN–PT–PZ ceramics were increased from 162 °C to 232 °C, as increasing the ZnO contents. When ZnO added, the k_p of specimens slightly was increased regardless Y₂O₃ contents. The mechanical quality factors were abruptly decreased regardless Y₂O₃ contents, when ZnO added until 0.75 wt.%. The optimized piezoelectric properties were obtained; d₃₃ = 730 (pC/N), k_p = 60, Q_m = 50, and  = 4750, when PMW–PNN–PT–PZ + 0.3 wt.% Y₂O₃ + 0.5 wt.% ZnO sintered at 1200 °C for 1 h.     

Effects of pyrolysis processes on the microstructures and mechanical properties of Cf/SiC composites using polycarbosilane

Three-dimensional braided carbon fiber reinforced silicon carbide composites (3D-B C_f/SiC) were prepared through eight cycles of vacuum infiltration of polycarbosilane (PCS) and subsequent pyrolysis under an inert atmosphere. The influences of heating rate and pyrolysis temperature on the microstructure and mechanical properties of C_f/SiC were discussed. It was found that the heating rate had great effect on the mechanical properties of C_f/SiC composites. With the increase of heating rate, the density of C_f/SiC composites increased and the interfacial bonding was weakened. As a result, the flexural strength of C_f/SiC was enhanced from 145 to 480 MPa when the heating rate was increased from 0.5 to 15 °C/min. The results showed that the flexural strength of the C_f/SiC composites fabricated at a heating rate of 15 °C/min could be increased from 480 to 557 MPa if the pyrolysis temperature of the sixth cycle was elevated from 1200 to 1600 °C, which was also attributed to the desirable interfacial structure and increased density. When tested at 1300 °C in vacuum, the C_f/SiC showed higher flexural strength (680 MPa) than that (557 MPa) at room temperature.     

Additive manufacturing of carbon fiber reinforced thermoplastic composites using fused deposition modeling

Additive manufacturing (AM) technologies have been successfully applied in various applications. Fused deposition modeling (FDM), one of the most popular AM techniques, is the most widely used method for fabricating thermoplastic parts those are mainly used as rapid prototypes for functional testing with advantages of low cost, minimal wastage, and ease of material change. Due to the intrinsically limited mechanical properties of pure thermoplastic materials, there is a critical need to improve mechanical properties for FDM-fabricated pure thermoplastic parts. One of the possible methods is adding reinforced materials (such as carbon fibers) into plastic materials to form thermoplastic matrix carbon fiber reinforced plastic (CFRP) composites those could be directly used in the actual application areas, such as aerospace, automotive, and wind energy. This paper is going to present FDM of thermoplastic matrix CFRP composites and test if adding carbon fiber (different content and length) can improve the mechanical properties of FDM-fabricated parts. The CFRP feedstock filaments were fabricated from plastic pellets and carbon fiber powders for FDM process. After FDM fabrication, effects on the tensile properties (including tensile strength, Young's modulus, toughness, yield strength, and ductility) and flexural properties (including flexural stress, flexural modulus, flexural toughness, and flexural yield strength) of specimens were experimentally investigated. In order to explore the parts fracture reasons during tensile and flexural tests, fracture interface of CFRP composite specimens after tensile testing and flexural testing was observed and analyzed using SEM micrograph.     

Influence of crystal orientation on ECAP of aluminum single crystals

A single crystal of high purity aluminum, oriented with the {1 1 1} slip plane and the 1 1 0 slip direction rotated by 20° in a clockwise sense from the theoretical shear plane and the shear direction, was processed by equal-channel angular pressing (ECAP) through a single pass. This configuration was designated the 20° orientation and the results are compared with earlier data obtained on a similar high purity aluminum single crystal in the 0° orientation with the (1 1 1) slip plane and the 1 1 0 slip direction lying parallel to the shear plane and the shear direction. The results show that in both orientations the long axes of the subgrains lie parallel to the slip traces of the primary slip system and the average subgrain widths are 1.3 μm. However, the shearing characteristics are different because the 0° specimen exhibited a conventional B-type rolling texture whereas the 20° specimen deformed by slip on the primary slip system and this system rotated by 40° in a counter-clockwise sense as the specimen passed through the shear zone of the ECAP die.     

CVD SiC fiber-reinforced barium aluminosilicate glass—ceramic matrix composites

Unidirectional CVD SiC (SCS-6) monofilament reinforced BaOAl₂O₃2SiO₂(BAS) glass—ceramic matrix composites have been fabricated by a tape lay-up method followed by hot pressing. The glass matrix flows around fibers during hot pressing resulting in nearly fully dense (95–98%) composites. Strong and tough composites having first matrix cracking stress of 250–300 MPa and ultimate flexural strength as high as 900 MPa have been obtained. Composite fracture surfaces showed fiber pullout with no chemical reaction at the fiber/matrix interface. From fiber push out, the fiber/matrix interfacial debond strength and the sliding frictional stress were determined to be 5.9 ± 1.2 MPa and 4.8 ± 0.9 MPa, respectively. The fracture surface of an uncoated SiC (SCS-0)/BAS composite also showed fiber/matrix debonding, fiber pullout, and crack deflection around the fibers implying that the SiC fibers may need no surface coating for reinforcement of the BAS glass-ceramic. Applicability of micromechanical models in predicting the first matrix cracking stress and the ultimate strength of these composites has also been examined.     

Structural and optical properties of (100 − x)(Li2B4O7) − x(SrO–Bi2O3–0.7Nb2O5–0.3V2O5) glasses and glass nanocrystal composites

Glasses of various compositions in the system (100 − x)(Li₂B₄O₇) − x(SrO–Bi₂O₃–0.7Nb₂O₅–0.3V₂O₅) (10  x  60, in molar ratio) were prepared by splat quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses (DTA). The amorphous nature of the as-quenched glasses and crystallinity of glass nanocrystal composites were confirmed by X-ray powder diffraction studies. Glass composites comprising strontium bismuth niobate doped with vanadium (SrBi₂(Nb_0.7V_0.3)₂O_9−δ (SBVN)) nanocrystallites were obtained by controlled heat-treatment of the as-quenched glasses at 783 K for 6 h. High resolution transmission electron microscopy (HRTEM) of the glass nanocrystal composites (heat-treated at 783 K/6 h) confirm the presence of rod shaped crystallites of SBVN embedded in Li₂B₄O₇ glass matrix. The optical transmission spectra of these glasses and glass nanocrystal composites of various compositions were recorded in the wavelength range 190–900 nm. Various optical parameters such as optical band gap (E_opt), Urbach energy (ΔE), refractive index (n), optical dielectric constant and ratio of carrier concentration to the effective mass (N/m^*) were determined. The effects of composition of the glasses and glass nanocrystal composites on these parameters were studied.     

Micromechanical analysis of fiber and titanium matrix interface by shear lag method

The model based on fracture mechanics is developed to evaluate the fracture toughness Γ of the fiber/matrix interface in titanium alloys reinforced by SiC monofilaments. Theoretical model for single fiber push-out testing is obtained by shear-lag method. The influences of several key factors (such as the applied stress needed for crack advance, crack length, and interfacial frictional shear stress) are discussed. Using the model, the interfacial toughness of typical composites including Sigma1240/Ti-6-4, SCS-6/Ti-6-4, SCS-6/Timetal 834, SCS-6/Timetal 21s, SCS-6/Ti-24-11 and SCS-6/Ti-15-3 are successfully predicted compared with previous results of these composites. It is verified that the model can reliably predict the interfacial toughness of the titanium matrix composites as well as other metal matrix composites, due to interfacial debonding usually occurs at the bottom face of the samples in such composites.     

Toughness,flexural, damping and interfacial properties of hybridized GFRE composites with MWCNTs

As the improved damping in fiber-reinforced composites can affect the other mechanical properties, therefore, the aim of this work is to investigate the effect of multiwall carbon nanotube (MWCNT) on the interfacial bond strength, flexural strength and stiffness, toughness and damping properties of hybridized glass-fiber reinforced epoxy (GFRE) composites. Nanophased epoxy resin was used to hybridize unidirectional and quasi-isotropic GFRE composites with [0/±45/90]_s and [90/±45/0]_s stacking sequences. Results from the interfacial characterizations of the hybridized composites showed improvement up to 30% compared to the control laminates. Hybridization of GFRE laminates with MWCNTs leads to decreasing the flexural and storage moduli, increasing flexural strength, toughness, natural frequencies and damping ratio. A high correlation coefficient of 0.9985 was obtained between static flexural and dynamic storage moduli. The highest flexural strength, flexural and storage moduli and natural frequency of quasi-isotropic laminate were observed for [0/±45/90]_s stacking sequence and vice versa for damping ratio.     

A 600 kV 15 mA Cockcroft–Walton high-voltage power supply with high stability and low-ripple voltage

A Cockcroft–Walton high-voltage power supply with high stability and low-ripple voltage has been developed. This power supply has been operated in a ns pulse neutron generator. The maximum non-load voltage is 600 kV while the working voltage and load current are 550 kV and 15 mA, respectively. The tested results indicate that when the power supply is operated at 300 kV, 6.7 mA and the input voltage varies ±10%, the long-term stability of the output voltage is S=(0.300–1.006)×10^-3. The ripple voltage is at 300 kV, 6.8–8.3 mA and the ratio of δU_P−P to the output voltage V_H is δU_P-P/V_H=2.1×10^-5.     

Effects of heat treatments on the microstructures and mechanical properties of Mg–3Nd–0.2Zn–0.4Zr (wt.%) alloy

Microstructure and mechanical properties of as-cast and different heat treated Mg–3Nd–0.2Zn–0.4Zr (wt.%) (NZ30K) alloys were investigated. The as-cast alloy was comprised of magnesium matrix and Mg₁₂Nd eutectic compounds. After solution treatment at 540 °C for 6 h, the eutectic compounds dissolved into the matrix and small Zr-containing particles precipitated at grain interiors. Further aging at low temperatures led to plate-shaped metastable precipitates, which strengthened the alloy. Peak-aged at 200 °C for 10–16 h, fine β″ particles with DO₁₉ structure was the dominant strengthening phase. The alloy had ultimate tensile strength (UTS) and elongation of 300–305 MPa and 11%, respectively. Aged at 250 °C for 10 h, coarse β′ particles with fcc structure was the dominant strengthening phase. The alloy showed UTS and elongation of 265 MPa and 20%, respectively. Yield strengths (YS) of these two aged conditions were in the same level, about 140 MPa. Precipitation strengthening was the largest contributor (about 60%) to the strength in these two aged conditions. The hardness of aged NZ30K alloy seemed to correspond to UTS not YS.     

Variation in the reaction zone and its effects on the strength of diffusion bonded titanium–stainless steel couple

Solid state bonding was carried out between commercially pure titanium and 304 stainless steel at 850 °C temperature for 30–150 min under uniaxial load in vacuum. The transition joints were characterized using optical and scanning electron microscopes and revealed the presence of reaction layers in the diffusion zone. The chemical composition of these reaction products was determined by energy dispersive spectroscopy and the presence of phase/phase mixtures σ, -Fe + χ, χ + λ, λ + FeTi + β-Ti and β-Ti were predicted. Their existence was also confirmed by X-ray diffraction technique. The concentration–penetration plots for Ti, Fe, Cr and Ni are obtained from electron probe microanalysis, which also exhibit concentration gaps in the profile indicating formation of intermetallics in the diffusion zone. The width of intermetallic phases attains its maximum for 90 min joining time, then drops and again rises for 150 min bonding time. The maximum bond strength of 76% of that of titanium was achieved for the assemblies processed for 90 min owing to better coalescence of the mating surfaces, though the volume fraction of intermetallics is high.