Structure property relation of hybrid biocomposites based on jute,viscose and polypropylene: The effect of the fibre content and the length on the fracture toughness and the fatigue properties

In the present study, the extent of jute and viscose fibre breakage during the extrusion process on the fracture toughness and the fatigue properties was investigated. The composite materials were manufactured using direct long fibre thermoplastic (D-LFT) extrusion, followed by compression moulding. The fracture toughness (K_IC) and the fracture energy (G_IC) of the PP–J30 composites were significantly improved (133% and 514%, respectively) with the addition of 10 wt% viscose fibres, indicating hindered crack propagation. The addition of viscose fibres resulted in three times higher fatigue life compared with that of the unmodified jute composites. Further, with the addition of (2 wt%) MAPP, the PP–J30–V10 resulted in a higher average viscose fibre length of 8.1 mm, and the fracture toughness and fracture energy increased from 9.1 to 10.0 MPa m^1/2 and 28.9 to 31.2 kJ/m², respectively. Similarly, the fatigue life increased 51% compared with the PP–J30–V10, thus demonstrating the increased work energy due to hindrance of the propagation of cracks.     

Fatigue and wear evaluation of Ti-Al-Nb alloys for biomedical applications

In this work the fatigue and wear behavior of Ti–15Al–33Nb(at.%) and Ti–21Al–29Nb(at.%) was evaluated and compared to that for other titanium-based biomedical implant alloys, in particular Ti–6Al–4V(wt.%). Fatigue stress versus life curves were obtained for tests performed at room temperature in air at a stress ratio of R = 0.1 for maximum stresses between 75%–90% of the ultimate tensile strength. The results indicated that the fatigue strength and lives of the as-processed alloys are comparable to that for Ti–6Al–4V(wt.%). Heat treatment significantly increased the orthorhombic-phase volume fractions in the alloys and resulted in reduced fatigue strength. The wear resistance for the alloys was significantly greater than that for Ti–6Al–4V(wt.%). Based on the current results, it is proposed that titanium–aluminum–niobium alloys will be of considerable future interest for biomedical applications.     

High-temperature dielectric and electromagnetic interference shielding properties of SiCf/SiC composites using Ti3SiC2 as inert filler

Ti₃SiC₂ filler has been introduced into SiC_f/SiC composites by precursor infiltration and pyrolysis (PIP) process to optimize the dielectric properties for electromagnetic interference (EMI) shielding applications in the temperatures of 25–600 °C at 8.2–12.4 GHz. Results indicate that the flexural strength of SiC_f/SiC composites is improved from 217 MPa to 295 MPa after incorporating the filler. Both the complex permittivity and tan δ of the composites show obvious temperature-dependent behavior and increase with the increasing temperatures. The absorption, reflection and total shielding effectiveness of the composites with Ti₃SiC₂ filler are enhanced from 13 dB, 7 dB and 20 dB to 24 dB, 21 dB and 45 dB respectively with the temperatures increase from 25 °C to 600 °C. The mechanisms for the corresponding enhancements are also proposed. The superior absorption shielding effectiveness is the dominant EMI shielding mechanism. The optimized EMI shielding properties suggest their potentials for the future shielding applications at temperatures from 25 °C to 600 °C.     

Reprint of “Multiaxial fatigue property of Ti–6Al–4V using hollow cylinder specimen under push-pull and cyclic inner pressure loading”

This paper studies a multiaxial fatigue crack mode and a fatigue life of Ti–6Al–4V. Load controlled fatigue tests at room temperature were carried out using a hollow cylinder specimen under multiaxial loading with principal stress ratio λ equal to 0, 0.4, 0.5 and 1.0 and loading ratio R kept constant and equal to 0. λ is defined as λ = σ₂/σ₁, where σ₁ and σ₂ are maximum and intermediate/minimum principal stresses, respectively. Here, the test at λ = 0 is a uniaxial loading test and that at λ = 1.0 an equi-biaxial loading test. A testing machine employed was a newly developed multiaxial fatigue testing machine which can apply push-pull and reversed torsion loading with inner pressure into the hollow cylinder specimen. Based on the obtained results in this study, multiaxial fatigue properties are examined, where the fatigue life evaluation and the crack mode are discussed. The fatigue life is reduced with an increase of λ, due to cyclic ratcheting and crack mode in multiaxial loading. The crack mode is also affected by the surface condition resulting from cut-machining.     

Effect of in situ synthesized TiB whisker on microstructure and mechanical properties of carbon–carbon composite and TiBw/Ti–6Al–4V composite joint

Carbon–carbon composite (C–C composite) and TiB whiskers reinforced Ti–6Al–4V composite (TiB_w/Ti–6Al–4V composite) were brazed by Cu–Ni + TiB₂ composite filler. TiB₂ powders have reacted with Ti which diffused from TiB_w/Ti–6Al–4V composite, leading to formation of TiB whiskers in the brazing layer. The effects of TiB₂ addition, brazing temperature, and holding time on microstructure and shear strength of the brazed joints were investigated. The results indicate that in situ synthesized TiB whiskers uniformly distributed in the joints, which not only provided reinforcing effects, but also lowered residual thermal stress of the joints. As for each brazing temperature or holding time, the joint shear strength brazed with Cu–Ni alloy was lower than that of the joints brazed with Cu–Ni + TiB₂ alloy powder. The maximum shear strengths of the joints brazed with Cu–Ni + TiB₂ alloy powder was 18.5 MPa with the brazing temperature of 1223 K for 10 min, which was 56% higher than that of the joints brazed with Cu–Ni alloy powder.     

Hot tensile behavior of an extruded Al–Zn–Mg–Cu alloy in the solid and in the semi-solid state

This is the first reported research into the tensile behavior of as-deformed Al–Zn–Mg–Cu alloy in the semi-solid state. Tensile tests of extruded 7075 aluminium alloy were carried out in the high temperature solid and semi-solid states. Based on the tensile results and microstructural examination, the tensile behavior can be divided into three stages according to the effect of liquid: one behaves in predominantly ductile character between 400 and about 520 °C (f_l ∼ 0.31%), one is governed by both of solid and liquid between 520 and 550 °C (f_l ∼ 2%), and almost completely dominated by liquid above ∼550 °C. A brittle temperature range (519–550 °C) is proposed, in which the as-deformed Al–Zn–Mg–Cu alloy exhibits large crack probability. An equation based on ultimate tensile stress and temperature is proposed.     

Multiaxial fatigue property of Ti–6Al–4V using hollow cylinder specimen under push-pull and cyclic inner pressure loading

This paper studies a multiaxial fatigue crack mode and a fatigue life of Ti–6Al–4V. Load controlled fatigue tests at room temperature were carried out using a hollow cylinder specimen under multiaxial loading with principal stress ratio λ equal to 0, 0.4, 0.5 and 1.0 and loading ratio R kept constant and equal to 0. λ is defined as λ = σ₂/σ₁, where σ₁ and σ₂ are maximum and intermediate/minimum principal stresses, respectively. Here, the test at λ = 0 is a uniaxial loading test and that at λ = 1.0 an equi-biaxial loading test. A testing machine employed was a newly developed multiaxial fatigue testing machine which can apply push-pull and reversed torsion loading with inner pressure into the hollow cylinder specimen. Based on the obtained results in this study, multiaxial fatigue properties are examined, where the fatigue life evaluation and the crack mode are discussed. The fatigue life is reduced with an increase of λ, due to cyclic ratcheting and crack mode in multiaxial loading. The crack mode is also affected by the surface condition resulting from cut-machining.     

Mechanical properties of Ti–4.5Al–3V–2Mo–2Fe and possibility for healthcare applications

The mechanical properties of Ti–4.5Al–3V–2Mo–2Fe, a relatively low cost titanium alloy originally designed for structural applications (especially for aerospace applications), were investigated. The alloy was subjected to heat treatments with various solution treatment temperatures (annealing temperature) and cooling rates. The mechanical properties of the heat-treated alloys were then used in order to judge the prospects of practical usage of the alloy for healthcare equipment such as wheelchairs.The mechanical properties of Ti–4.5Al–3V–2Mo–2Fe are highly affected by either solution treatment or cooling rate, and they change as a result of the change in the microstructure. The alloy single annealed at temperature in the α + β field has very high fatigue ratio (0.80–0.85) and high specific strength (210–260 MPa/g cm^− 3) with a modest fracture toughness (J_IC = 25–35 kN/m). This balance of fatigue ratio and specific strength is better than that of the existing wheelchair materials.Thus, from the point of view of mechanical properties, Ti–4.5Al–3V–2Mo–2Fe has high potential to be used for healthcare applications.     

Tensile and fatigue evaluation of Ti–15Al–33Nb (at.%) and Ti–21Al–29Nb (at.%) alloys for biomedical applications

In this work the fatigue and tensile behavior of Ti–15Al–33Nb (at.%) and Ti–21Al–29Nb (at.%) was evaluated and compared to that for other titanium-based biomedical implant alloys, in particular Ti–6Al–4V (wt.%). The mechanical properties of interest were fatigue strength, tensile strength, elastic modulus, and elongation-to-failure. Fatigue stress versus life curves were obtained for tests performed at room temperature in air as well as in Ringer's solution at R = 0.1 for maximum stresses between 35% and 90% of the ultimate tensile strength. The results indicated that the fatigue strength and lives and elastic modulus of these alloys is comparable to that for Ti–6Al–4V (wt.%). Considering the data scatter and deformation behavior, the Ringer's solution did not significantly affect the fatigue behavior. Heat treatment reduced the tensile strength and this corresponded to a reduction in the fatigue strength. The tensile strength of the as-processed Ti-Al-Nb alloys was slightly lower than that for Ti–6Al–4V (wt.%), and the Ti–15Al–33Nb (at.%) exhibited lower strengths and higher elongations than Ti–21Al–29Nb. Based on the current results, it is proposed that titanium–aluminum–niobium alloys will be of considerable future interest for biomedical applications.     

Thermomechanical fatigue of titanium aluminides

This paper reviews the thermomechanical fatigue (TMF) studies performed on various titanium aluminide (TiAl) alloys during the last decade in the research group of one of the authors (H.-J. Christ). The investigated alloys are Ti–47Al–2Mn–2Nb (XD), Ti–46Al–4(Cr, Nb, Ta, B) (γ-MET), Ti–45Al–5Nb–0.2C–0.2B (TNB-V5) and Ti–45Al–8Nb–0.2C (TNB-V2). An interesting result of this comparison is that the materials, though different in chemical compositions, yield comparable TMF behaviour. It can be demonstrated that both out-of-phase (OP) and in-phase (IP) TMF life depend on mean stress σ_m, which is primarily determined by the temperature-strain phasing, but also strongly affected by total strain amplitude Δε/2, maximum temperature T_max and temperature interval ΔT – highest mean stresses (i.e. compressive σ_m in the case of IP-TMF, tensile σ_m for OP-TMF) resulted in lowest TMF lives. Furthermore, the investigation reveals that the ratio between IP and OP fatigue lives under corresponding conditions can be expressed as a function of the temperature range ΔT. At low values of ΔT the ratio is rather small because the material’s fatigue behaviour approaches isothermal conditions. Higher strain and temperature amplitudes result in very high ratios between IP and OP lives. The influence of cyclic hardening at low temperature during IP-TMF applying a very large ΔT seems to reduce the fatigue life ratio again, because of the rather high stress amplitude established.     

The effect of fabrication processes on the mechanical and interfacial properties of SiCf/Cu–matrix composites

Three groups of SiC_f/Ti/Cu composites were prepared under conditions of 650 °C + 105 min (sample 1#), 750 °C + 85 min (sample 2#) and 840 °C + 50 min (sample 3#), respectively, by foil-fiber-foil method (FFF), and their room temperature tensile strengths were established. The aim is to model the reactive bonding states between Ti and SiC fiber and between Ti and Cu when Ti is used as interfacial adhesion promoters in SiC_f/Cu–matrix composites. The fracture surfaces, SiC_f/Ti interfaces and Ti/Cu interfaces were investigated by scanning electron microscopy (SEM), optical microscopy and energy dispersive spectroscopy (EDS). The tensile tests show that the tensile strengths of samples 1# and 2# are not obviously enhanced due to the weak bonding strength between SiC fiber and Ti, while those of sample 3# are achieved above 90% of ROM (the rule of mixtures) strength because of excellent bonding between SiC fiber and Ti. However, there are distinct Ti/Cu interfacial reaction zones after the three processes, which are approximately 5.4, 9.0 and 13.3 μm thick, respectively. The Ti/Cu interfacial reaction products are mainly distributed in four layers. In samples 1# and 2#, the products are predicted to be Cu₄Ti, Cu₃Ti₂, CuTi and CuTi₂ according to their chemical compositions determined by EDS, while in sample 3#, the products are Cu₄Ti, Cu₄Ti₃, CuTi and CuTi₂. Additionally, the relationships between the thickness of Ti interlayer and its reaction with C and Cu are also discussed, and an optimal thickness of Ti is introduced.     

A micromechanical cyclic void growth model for ultra-low cycle fatigue

The influence of stress triaxiality and Lode parameter on microvoid growth phase of ductile fracture under ultra-low cycle fatigue (ULCF) (N_f < 100, N_f = cycles to failure) loading is investigated using micromechanical analyses. A new micromechanical cyclic void growth model (MM-CVGM) to predict the ULCF life of ASTM A992 steels is presented. The MM-CVGM is calibrated and validated from the experiments conducted on axisymmetrically notched specimens. Number of cycles to failure (N_f) and the fracture initiation locations predicted by the model closely matched the experimental observations.     

Effect of transition metals on energy absorption during strain-controlled fatigue of an aluminum alloy

Tensile and low cyclic fatigue tests were used to assess the influence of micro-additions of Ti/V/Zr on the performance of Al–7Si–1Cu–0.5Mg (wt.%) alloys in the as-cast and T6 heat-treated conditions and their improvement was compared to the base alloy. The microstructure of the as-cast Al–7Si–1Cu–0.5Mg (wt.%) base and modified alloys consisted of α-Al, eutectic Si, and Cu, the Mg- and Fe-based phases Al_2.1Cu, Al_8.5Si_2.4Cu, Al_7.2Si_8.3Cu₂Mg_6.9 and Al₁₄Si_7.1FeMg_3.3. In addition, the micro-sized Ti/V/Zr-rich phases Al_6.8Si_1.4Ti, Al_21.4Si_4.1Ti_3.5VZr_3.9, Al_6.7Si_1.2TiZr_1.8, Al_2.8Si_3.8V_1.6Zr and Al_5.1Si_35.4Ti_1.6Zr_5.7Fe were identified in the modified alloys. It was also noticed that increasing the content of Ti–V–Zr changed the morphology of Ti/V/Zr-rich phase. The tensile test results showed that the T6 heat-treated alloy modified with the addition of a higher content of Ti–V–Zr achieved the highest tensile strength of 343 MPa over the base alloy and alloys modified with additions of Ti, Ti–Zr and lower contents of Ti–V–Zr. The plastic strain energy density coefficient of the alloy modified with the addition of a higher content of Ti–V–Zr in the T6 temper condition was higher than the other studied alloys and reached 162 MJ m⁻³. The fatigue life of the same alloy was considerably longer than that of the other studied alloys, including the base alloy. The fractography revealed that all the studied alloys showed similar fracture behavior. The tensile cracks propagated through the eutectic Si and primary phases, exhibiting intergranular fracture along with some cleavage-like features of the plate-shaped Zr–Ti–V-rich intermetallics with the presence of fatigue striations on the latter, indicating their ductile nature. It is believed that the morphological changes of intermetallic precipitates containing Zr, Ti and V enhance the fatigue life of the alloy modified with additions of larger amounts of Ti–V–Zr in the T6 condition.     

Microstructural and mechanical properties of jointed ZrO2/Ti–6Al–4V alloy using Ti33Zr17Cu50 amorphous brazing filler

Ceramic ZrO₂ and metallic Ti–6Al–4V alloy are jointed by using a Ti₃₃Zr₁₇Cu₅₀ (at.%) amorphous alloy as a solder at 1123–1273 K in a high vacuum. It is demonstrated that the microstructure and mechanical properties are significantly influenced by the brazing temperature, the heat time and the cooling rate. The brazing seam jointing ZrO₂ with Ti–6Al–4V is composed of ZrO₂/Cu₂Ti₄O, (Ti,Zr)₂Cu/TiO, Ti₂O/CuTi₂, (Ti,Zr)₂Cu/CuTi₂/Ti–6Al–4V alloys and compounds, of which the increasing thickness weakens the shear strength as the brazing temperature, the heat time the cooling rate increase. The maximum shear strength of the brazing joints reaches 162 MPa with the optimal technical parameters: the brazing temperature of 1173 K, the heat time of 10 min and the cooling rate of 5 K/min. The fracture of the joint occurs in the brittle seam layer nearby the side of ZrO₂.     

Experimental study of diffusion welding/bonding of titanium to copper

In the present study, Ti–6Al–4V alloy was bonded to electrolytic copper at various temperatures of 875, 890 and 900 °C and times of 15, 30 and 60 min through diffusion bonding. 3 MPa uniaxial load was applied during the diffusion bonding. Interface quality of the joints was assessed by microhardness and shear testing. Also, the bonding interfaces were analysed by means of optical microscopy, scanning electron microscopy and energy dispersive spectrometer. The bonding of Ti–6Al–4V to Cu was successfully achieved by diffusion bonding method. The maximum shear strength was found to be 2171 N for the specimen bonded at 890 °C for 60 min. The maximum hardness values were obtained from the area next to the interface in titanium side of the joint. The hardness values were found to decrease with increasing distance from the interface in titanium side while it remained constant in copper side. It was seen that the diffusion transition zone near the interface consists of various phases of βCu₄Ti, Cu₂Ti, Cu₃Ti₂, Cu₄Ti₃ and CuTi.     

Fatigue fracture of friction-stir processed Al–Al3Ti–MgO hybrid nanocomposites

This paper presents experimental results on the fatigue properties of Al-matrix nanocomposites prepared by the friction stir processing (FSP) technique. An Al–Mg alloy (AA5052) with different amounts (∼2 and 3.5 vol%) of pre-placed TiO₂ nanoparticles were FSPed up to 6 passes to attain homogenous dispersion of nano-metric inclusions. Microstructural studies by electron microscopic and electron back scattering diffraction (EBSD) techniques showed that nano-metric Al₃Ti (50 nm), TiO₂ (30 nm), and MgO (50 nm) particles were distributed throughout a fine-grained Al matrix (<2 μm). Consequently, a significant improvement in the tensile strength and hardness was attained. Uniaxial stress-controlled tension–tension fatigue testing (R = 0.1) were utilized to evaluate the fatigue behavior of the prepared nanocomposites. The results were compared with the un-processed (annealed) and FSPed alloy without pre-placing TiO₂ particles. It was found that FSP of the aluminum alloy increased the fatigue strength (at 10⁷ cycles) for about 28% and 32% compared with the annealed specimen when the concentration of the reinforcing particles was 2 and 3.5 vol%, respectively. Fractographic analysis determined a ductile fracture behavior with deep-equiaxed dimples for the annealed and FSPed alloy. The facture surface of the nanocomposites revealed a combined ductile–brittle fracture mode with finer dimples. The mechanism of the fatigue fracture and the role of nano-metric inclusions were elaborated.     

Interfacial structure and fracture behavior of 6061 Al and MAO-6061 Al direct active soldered with Sn–Ag–Ti active solder

Micro-arc oxidation (MAO), a novel coating method capable of depositing compact, ultra-hard ceramic composite coatings on Al and its alloys, is applied to heat sink surfaces. A micro-porous Al₂O₃ layer was synthesized on 6061 Al-Alloy (MAO–Al) using the MAO technique. The microstructure, shear strength and fracture of Al/Al, MAO–Al/MAO–Al, and Al/MAO–Al joints were determined after direct active soldering in air with the Sn3.5Ag4Ti(Ce) active solder at 250 °C for 30 s. During active soldering, Al dissolves into SAT solder to form a coarse Al–Ag–Sn solid solution around the solder. Also, the active element Ti concentrates to and reacts with the MAO–Al layer to form both Ti-oxidized (e.g., TiO and TiO₂) or rich-Ti(Al,Sn)₃, and subsequently Ag₃Sn nanoparticles are adsorbed at the solder/MAO–Al interfaces. The shear-tested bonding strengths were 15.3 ± 1.38 MPa for Al/Al, 10.45 ± 1.53 MPa for MAO–Al/Al, and 8.25 ± 1.53 MPa for MAO–Al/MAO–Al joints. In the Al/Al specimen, the fracture occurred in Al–Ag–Sn compounds of the active matrix after shear testing. In the MAO–Al/MAO–Al and MAO–Al/Al specimens, the fracture occurred in the MAO–Al/active solder interface.     

The effect of different methods to add nitrogen to titanium alloys on the properties of titanium nitride clad layers

In this investigation, titanium nitride (TiN) reinforcements are synthesized in situ on the surface of Ti–6Al–4V substrates with gas tungsten arc welding (GTAW) process by different methods to add nitrogen, nitrogen gas or TiN powder, to titanium alloys. The results showed that if nitrogen gas was added to titanium alloys, the TiN phase would be formed. But if TiN powder was added to titanium alloys, TiN + TiN_x dual phases would be presented. The results of the dry sliding wear test revealed that the wear performance of the Ti–6Al–4V alloy specimen coated with TiN or TiN + TiN_x clad layers were much better than that of the pure Ti–6Al–4V alloy specimen. Furthermore, the evolution of the microstructure during cooling was elucidated and the relationship among the wear behavior of the clad layer, microstructures, and microhardness was determined.     

Surface treatment of new type aluminum lithium alloy and fatigue crack behaviors of this alloy plate bonded with Ti–6Al–4V alloy strap

Samples consisting of new aluminum lithium alloy (Al–Li alloy) plate developed by the Aluminum Company of America and Ti–6Al–4V alloy (Ti alloy) plate were investigated. Plate of 400 mm × 140 mm × 2 mm with single edge notch was anodized in phosphoric solution and Ti alloy plate of 200 mm × 20 (40) mm × 2 mm was anodized in alkali solution. Patterns of two alloys were studied at original/anodized condition. And then, aluminum alloy and Ti alloy plates were assembled into a sample with FM 94 film adhesive. Fatigue crack behaviors of the sample were investigated under condition of nominal stress σ = 36 MPa and 54 MPa, stress ratio of 0.1. Testing results show that anodization treatment modifies alloys surface topography. Ti alloy bonding to Al–Li alloy plate effectively retards crack growth than that of Al–Li alloy plate. Fatigue life of sample bonded with Ti alloy strap improves about 62.5% than that of non-strap plate.     

An investigation on microstructure and mechanical properties of Al7075 to Ti–6Al–4V Transient Liquid Phase (TLP) bonded joint

Transient Liquid Phase (TLP) bonding of two dissimilar alloys Al7075 and Ti–6Al–4V has been done at 500 °C under 5 × 10⁻⁴ torr. Cu was electrodeposited on Al7075 and Ti–6Al–4V surfaces, 50 μm thick Sn–4Ag–3.5Bi film was used as interlayer and bonding process was carried out at several bonding times. The microstructure of the diffusion bonded joints was evaluated by Light Optical Microscopy (LOM), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The eutectic and intermetallic compounds formation along Al7075 grain boundaries and Ti/Al interface such as θ(Al₂Cu), TiAl and Ti₃Al were responsible for joint formation at the aluminum and titanium interfaces. Microhardness and shear strength tests were used to investigate the mechanical properties of the bonds. Hardness of the joints increased with increasing bonding time which can be attributed to the intermetallics formation at the interface. The study showed that the highest bond strength was 36 MPa which was obtained for the samples joined for 60 min.