Mechanical and microstructural characterizations of ultrafine grained Zircaloy-2 produced by room temperature rolling

The effect of deformation strain at room temperature on the microstructural and mechanical properties of Zircaloy-2 was investigated in the present work. The sample was initially heat treated at 800 °C in argon environment and quenched in mercury prior to rolling. The deformed alloys were characterized by using EBSD and TEM. It reveals the misorientation of incidental grain boundaries (IDBs) due to large plastic strain induced in the sample. The recovery of deformed alloy upon annealing leads to the formation of ultrafine and nanostructured grains in the alloy. The hardness achieved after 85% room temperature rolling (RTR) is found to be 269 HV, while the tensile strength is 679 MPa and 697 MPa in the rolling and transverse direction, respectively. The improvement in strength is due to generation of high dislocation density and ultrafine grains in the deformed alloy with 85% thickness reduction, during rolling. The deformed alloy subjected to annealing at 400 °C for 30 min sample shows increase in ductility (6% and 7.2%) in rolling and transverse direction, respectively, due to the annihilation of dislocations as evident from the TEM study.     

Biodegradable green composites made using bamboo micro/nano-fibrils and chemically modified soy protein resin

Micro/nano-sized bamboo fibrils (MBF) and a modified soy protein resin were used to fabricate environmentally friendly composites. With the incorporation of MBF the fracture stress and Young’s modulus of the soy protein concentrate (SPC) increased significantly. With the addition of 30 parts of MBF (SPC is 100 parts, based on weight), the fracture stress and Young’s modulus were increased from 20.2 MPa to 59.3 MPa and from 596 MPa to 1816 MPa, respectively. The addition of MBF, however, did not show significant decrease in the fracture strain of the specimens. As a result, the toughness of the MBF reinforced SPC increased. The toughness of the SPC based composites containing 30 parts of MBF was 6.0 MPa compared to 2.7 MPa for SPC without MBF. MBF reinforced SPC was then cross-linked using a silane, (3-isocyanatopropyl)triethoxysilane (ITES). Although the fracture strength and Young’s modulus did not show significant increase, the modification using ITES showed significant increase in the fracture toughness. SPC containing 30 parts of MBF, 10 parts of ITES and 2 parts of glycerol showed fracture stress of 82 MPa, Young’s modulus of around 3.2 GPa and toughness of 4.3 MPa. The environment-friendly, fully biodegradable green composites, based on MBF and modified SPC resins, have excellent properties and great potential to replace the traditional petroleum-based materials in many applications.     

Fabrication of porous titanium scaffold with controlled porous structure and net-shape using magnesium as spacer

This paper reports a new approach to fabricating biocompatible porous titanium with controlled pore structure and net-shape. The method is based on using sacrificial Mg particles as space holders to produce compacts that are mechanically stable and machinable. Using magnesium granules and Ti powder, Ti/Mg compacts with transverse rupture strength (~ 85 MPa) sufficient for machining were fabricated by warm compaction, and a complex-shape Ti scaffold was eventually produced by removal of Mg granules from the net-shape compact. The pores with the average size of 132–262 μm were well distributed and interconnected. Due to anisotropy and alignment of the pores the compressive strength varied with the direction of compression. In the case of pores aligned with the direction of compression, the compressive strength values (59–280 MPa) high enough for applications in load bearing implants were achieved. To verify the possibility of controlled net-shape, conventional machining process was performed on Ti/Mg compact. Compact with screw shape and porous Ti scaffold with hemispherical cup shape were fabricated by the results. Finally, it was demonstrated by cell tests using MC3T3-E1 cell line that the porous Ti scaffolds fabricated by this technique are biocompatible.     

Research on the microstructure,fatigue and corrosion behavior of permanent mold and die cast aluminum alloy

Permanent mold (PM) and high pressure die cast (HPDC) AlMg5Si2Mn are employed to investigate the microstructure, fatigue strength and corrosion resistance. Results indicated that the mechanical properties (R_m, R_0.2 and δ) of HPDC specimens (314 MPa, 189 MPa and 7.3%) are significantly better than those of PM specimens (160 MPa, 111 MPa and 2.5%) due to the finer grain size and less cast defects. Fatigue cracks of PM samples dominantly initiated from shrinkage pores and obscure fatigue striations are observed in crack growth region. Corrosion and pitting potentials of PM and HPDC AlMg5Si2Mn alloy are around −1250 mV, −760 mV and −1220 mV, −690 mV respectively. Numerous pits are observed around the grain boundaries because the corrosion potential of Mg₂Si is more anodic than that of α-Al matrix. In addition, the superior corrosion resistance of HPDC samples can be attributed to the fine grain size and the high boundary density which improved the formation of oxide layer on the surface and prevented further corrosion.     

The effect of rolling direction on the creep process of Al–Cu bimetallic sheet

The study of the mechanical properties of aluminium–copper (Al–Cu) metal layered composite, formed by joining aluminium and copper sheets in the process of rolling have been presented in this paper. The influence of the rolling direction on the basic strength parameters and rheological properties of the composite was analysed. All tests were carried out on flat specimens cut from a sheet in the direction compatible with the rolling direction (RD) and transverse direction (TD). Preliminary tests of monotonic uniaxial tension at a temperature of 293 K were carried out and the basic mechanical properties of Al–Cu bimetal were determined. The hardening process of the material was described by the three-parameter Swift’s equation. The essential creep tests were carried out at a temperature of 523 K in the range of stress 88.5–137.9 MPa. The relation between minimum creep rate and applied stress for the specimens cut from the RD and TD directions were determined. The relationships between the time to fracture, stress, and rupture elongation, obtained from the creep tests, were determined as well. Variations of the steady creep rate with time to fracture by using the Monkman–Grant’s model and its modifications were analysed. It was found that the rolling process strongly affected the short-time monotonic deformation at 293 K and the creep process at 523 K temperature.     

Preparation of SiC ceramics by aqueous gelcasting and pressureless sintering

Gelcasting is an attractive forming process to fabricate ceramic parts with complex shape. In the present work, aqueous gelcasting of SiC was studied. SiC slurry (50 vol.%) for gelcasting was prepared with sintering assistants, Al₂O₃ and Y₂O₃. The slurry was solidified in situ to green body with relative density of 55.9 ± 0.9% and flexural strength of 13.9 ± 0.7 MPa. SEM shows that ceramic powders in green body compact closely by the connection of polymer networks, and that the pores decrease greatly with the size less than 1 μm. SiC samples were also obtained by the process of gelcasting and pressureless sintering at 2000 °C for 1 h in Ar atmosphere. The relative density and flexural strength of SiC sintered body are 97.3 ± 0.4% and 637 ± 156 MPa, and the hardness and toughness are 20.68 ± 0.80 GPa and 3.85 ± 0.23 MPa m^1/2, respectively.     

Effects of warm rolling and ageing after cryogenic rolling on mechanical properties and microstructure of Al 6061 alloy

The mechanical properties and microstructural evolution of Al 6061 alloy subjected to cryorolling and warm rolling have been investigated in the present work. The Al 6061 alloy was subjected to thickness reduction of 70% by cryorolling followed by thickness reduction of 20% by warm rolling. The cryorolled + warmrolled (CR + WR) samples were characterized by Electron back scattered diffraction (EBSD) technique, Differential scanning calorimetry (DSC), X-Ray diffraction (XRD) analysis and Transmission electron microscopy (TEM) technique to substantiate the role of deformation strain and temperature on their microstructural features and compared with cryorolled (CR) samples. The CR + WR samples showed a significant improvement in tensile strength (376 MPa) and partial improvement in ductility (5%) as measured from tensile testing. It is mainly due to the combined effect of partial grain refinement, solid solution strengthening, dislocation hardening, dynamic recovery, and dynamic ageing during cryorolling and warm rolling. The effect of ageing on CR + WR samples was investigated and the optimum ageing condition was found to be 45 h at 125 °C, which gives improved tensile strength of (406 MPa) and good tensile ductility (10%). The tensile strength of cryorolled + warm rolled + peak aged (CR + WR + PA) sample (406 MPa) was found to be 11.2% more than that of cryorolled + peak aged (CR + PA) sample (365 MPa). During peak ageing treatment, the strength has been retained by pinning of dislocations through nanosized precipitates generated during warm rolling and it has been improved further by precipitation of the remnant dissolved second phase in the matrix. However, the observed ductility of CR + PA sample was 13% more than CR + WR + PA sample due to low dislocation density after ageing.     

Tensile properties of hot rolled Mg–3Sn–1Ca alloy sheets at elevated temperatures

Mechanical behavior of hot rolled Mg–3Sn–1Ca (TX31) magnesium alloy sheets were studied in the temperature range 25–350 °C. The microstructure of the alloy consisted of the eutectic structure of α-Mg + Mg₂Sn and a dispersion of needle-like CaMgSn. The highest room-temperature ductility of 18% was obtained by hot rolling of the cast slabs at 440 °C, followed by annealing at 420 °C. The high temperature tensile deformation of the material was characterized by a decrease in work hardening exponent (n) and an increase in strain rate sensitivity index (m). These variations resulted in respective drops of proof stress and tensile strength from 126.5 MPa and 220 MPa at room temperature to 23.5 MPa and 29 MPa at 350 °C. This was in contrast to the ductility of the alloy which increased from 18% at room temperature to 56% at 350 °C. The observed variations in strength and ductility were ascribed to the activity of non-basal slip systems and dynamic recovery at high temperatures. The TX31 alloy showed lower strength than AZ31 magnesium alloy at low temperatures, while it exhibited superior strength at temperatures higher than 200 °C, mainly due to the presence of thermally stable CaMgSn particles.     

The characterization of shape memory effect for low elastic modulus biomedical β-type titanium alloy

This work investigates the textures of biomedical TiNbTaZr alloy rolled by 99% cold reduction ratios in thickness. The relationship between textures and superelasticity of the specimens treated at 873 K and 1223 K for 1.2 ks is studied. The microstructure of tensile specimen is investigated by transmission electron microscopy. Textures of cold-rolled and heat-treated specimens are studied. During unloading, the anisotropy of superelastic strain and pure elastic strain in the heat-treated specimens is observed. Superelastic strain along rolling direction and transverse direction is larger than those along 45° from rolling direction while pure elastic strain shows the highest value along 45° from rolling direction in the specimen treated at 873 K. For the specimen treated at 1223 K, higher pure elastic strain is obtained along rolling direction. The maximum recovered strain around 2.11% is obtained along rolling direction.     

Strength and toughness: The challenging case of TaC-based composites

This work aims at studying the relationships between strength and toughness of tantalum carbide (TaC) ceramics, a refractory ceramic used in aerospace and energy production sectors. The effect of different secondary phases was explored: (I) the addition of a transition metal silicide with suited thermo-elastic properties, TaSi₂, (II) the addition of SiC particles, platelets or fibers, and (III) chopped carbon fibers. Microstructural analyses, performed by scanning and transmission electron microscopy, were essential in revealing at nanoscale level the morphological changes occurred during sintering in the reinforcing phase and its interaction with matrix and sintering additive. Mechanisms of reinforcement evolution are suggested accordingly. Fracture toughness and flexural strength were measured and the values were compared to unreinforced materials and discussed in agreement to the microstructural features. Strength approaching 1 GPa was obtained upon addition of SiC particles, but residual thermal stresses prevented from notable increase of toughness, which fluctuated around 4 MPa √m. A good compromise between strength and toughness was found for addition of Hi-Nicalon SiC fiber, 550 MPa and 5.3 MPa √m, respectively. More refractory SiC fibers resulted not effective, owing to the rising of tensional state in the matrix. On the other hand, TaSi₂ led to a toughness of 4.7 MPa √m and strength around 680 MPa. Conversely, carbon fiber led to poor toughness due to unfavorable combination of coefficient of thermal expansion with the matrix.     

Vacuum heat treatment of iron parts produced by selective laser melting: Microstructure,residual stress and tensile behavior

Selective laser melted parts easily accumulate a large amount of residual stress due to their rapid heating and cooling, which is deleterious to their mechanical properties and limits their applications. In this work iron parts, as the basic industry material, were produced by the new emerging additive manufacturing technology, selective laser melting (SLM). SLM-fabricated iron parts were heat-treated under vacuum to eliminate the residual stress. Results have shown that the crystalline structure of iron (α-Fe) was not modified after the selective laser melting process and after the heat treatment. The broadening of XRD spectra appeared and the micro-stain decreased after the vacuum heat treatment. Columnar grains appeared in the building direction due to the temperature gradient in the molten pool during SLM process. After the vacuum annealing treatment, the grain refinement has occurred due to the residual stress as the driving force although a residual amount of the columnar microstructural architecture could be observed. Although the as-fabricated iron part possesses a higher tensile strength even than that of bulk iron material, the elastic modulus of the annealed specimens decreased to 188 ± 10 GPa and the ultimate tensile strength was much improved from 357 ± 22 MPa up to 401 ± 23 MPa. The yield strength increased from 256 ± 17 MPa up to 352 ± 21 MPa. By means of the micro-indentation method, the tensile residual stress was found in the as-fabricated iron sample.     

Temperature effects on the fracture behavior and tensile properties of silane-treated clay/epoxy nanocomposites

We investigated the effects of clay silane treatment on the fracture behaviors of clay/epoxy nanocomposites by comparing the compliance, critical fracture load, and fracture toughness of silane-treated samples with those of untreated samples. The fracture toughnesses of untreated and silane-treated clay/epoxy nanocomposites were 8.52 J/m² and 15.55 J/m², respectively, corresponding to an 82% increase in fracture toughness after clay silane treatment. Tensile tests were performed at ?30 °C, 25 °C, 40 °C, and 70 °C. Tensile strength and elastic modulus were higher at ?30 °C than at 25 °C for both samples. However, the tensile properties decreased as temperature increased for both samples. In particular, at 70 °C, the tensile properties were less than 10% of the original value at room temperature, independent of surface treatment. The fracture and tensile properties of silane-treated clay/epoxy nanocomposites increased due to good dispersion of the clay in epoxy and improvement in interfacial adhesive strength between epoxy and clay layers.     

In vivo osteocompatibility of lotus-type porous nickel-free stainless steel in rats

The bone response to lotus-type porous nickel-free stainless steels implants was investigated using Sprague-Dawley rats. The implants were inserted in the femora and tibiae of rats (n = 60) and bone formation inside the pores of the implants was followed up to 12 weeks. Bone ingrowth in transverse histological sections was calculated using an image analysis program. Shear strength of the bone–implant interface was evaluated by the push-out test. Histological examination showed that bone grew into apparent direct contact with the implant surface and into the pores, which sizes were between 70–650 μm. At 12 weeks, maximum compressive shear strengths of 24 ± 1 MPa were obtained; these values are substantially higher than the typical shear strength achieved by porous-coated materials. These results clearly indicate that lotus-type porous structure allowed bone cells and tissue to invade the implant throughout superficial porous spaces, which resulted in an efficient biological fixation responsible for the mechanical stability at the implantation site.     

Residual stress and strain in MIG butt welds in 5083-H321 aluminium: As-welded and fatigue cycled

This paper presents single-line residual stress profiles for 8 mm 5083-H321 aluminium plates joined by gas metal arc (MIG) welding. The data were obtained by synchrotron diffraction strain scanning. Weld metal stresses (up to ～7 mm either side of the centreline) are quite scattered and unreliable because of the large epitaxial grain size in the fusion zone. Peak magnitude of the transverse stresses varies between +50 MPa (19% of parent plate proof strength) at the HAZ boundary to ?150 MPa (57% of PP proof strength) at the weld centreline. Equivalent values for longitudinal stresses are +90 MPa (34% of PP proof strength) some 22 mm from the weld centreline to ?120 MPa (45% of PP proof strength) at the weld centreline. Plate-to-plate variation in the as-welded transverse and longitudinal residual stress values across the weld toe region is around 40 MPa. The effect on residual stress and strain values of a sequence of applied fatigue loads was also considered and reported.     

Development of carbon nanofiber reinforced hydroxyapatite with enhanced mechanical properties

In order to improve fracture toughness, carbon nanofibers (CNF) were used as reinforcement for hydroxyapatite (HA) composites. The powder mixture of CNF/HA were obtained with ball-milling technique. CNF/HA composites were sintered by hot-pressing with 7.81 and 15.6 MPa sintering pressure. Maximum sintering pressure was 1200 °C. Mechanical and physiological bio-compatibility were evaluated by four-point bending tests, indentation tests and immersion tests in simulated body fluid (SBF). The strength values of 10 vol.% CNF/HA composites sintered at 15.6 MPa is 90 MPa, which is within those of cortical bone. The fracture toughness values for CNF/HA composites are around 1.6 times higher than those obtained for HA. Equal bioactivity are obtained for CNF/HA composites.     

The effect of thermal cycling in superplastic diffusion bonding of 2205 duplex stainless steel

In view of the requirement of large cold rolling deformation and bonding pressure in the conventional superplastic diffusion bonding of 2205 duplex stainless steel, a novel method of introducing thermal cycling into the process was proposed. During the thermal cycling process, due to the change of temperature, surface chemical activity of 2205 duplex stainless steel was improved, activity of atoms and grain boundaries were improved, and the recrystallized grains were refined. The shear bond strength of joint prepared in the mode of thermal cycling using specimens with the cold roll reduction of 60% was 15 MPa higher than that of conventional bonding using specimens with the cold roll reduction of 85%. Compared to the shear bond strength of 430 MPa under the specific pressure of 10 MPa after conventional bonding, shear bond strength of 623 MPa was obtained under the condition of T_max = 1000 °C, T_min = 900 °C, cycle number of heating and cooling N = 3, and specific pressure P = 5 MPa.     

Effect of granulated sugar as pore former on the microstructure and mechanical properties of the vitrified bond cubic boron nitride grinding wheels

For vitrified bond cubic boron nitride (CBN) grinding wheel, introduced pores play a very important role for its mechanical properties and performance. In this paper, granulated sugar was used as pore former of the vitrified bond in CBN grinding wheel. The effects of content and particle size of the granulated sugar on the porosity and the flexural strength of the sintered vitrified bond CBN wheel samples have been investigated. It was found that the porosity of the vitrified bond CBN wheel is positively correlated with the content of the granulated sugar. The smaller and more irregular shaped pores are uniformly distributed in the bond when the content of granulated sugar is between 1 and 3 wt.%. Larger and more non-uniform pores and pore channels appear as the content of granulated sugar is increased from 5 to 7 wt.%. The flexural strength of the vitrified bond CBN wheel specimens decreases with an increase in pore former’s content and the porosity. With the increase of pore former’s particle size at the content of 3 wt.%, the flexural strength reaches to a peak value of 49 MPa with average particle size of granulated sugar is 250 μm. When the average size of granulated sugar is from 100 to 125 μm, the pores’ size is similar with the size of pore former and distributed homogeneously. The larger granulated sugar with the size from 160 to 500 μm can introduce different size of pores which could be smaller or larger than the size of pore former.     

Effects of SiC interphase by chemical vapor deposition on the properties of C/ZrC composite prepared via precursor infiltration and pyrolysis route

Silicon carbide (SiC) interphase was introduced by chemical vapor deposition (CVD) process to prevent carbon fiber degradation and improve fiber–matrix interface bonding of C/ZrC composite prepared via precursor infiltration and pyrolysis (PIP) process. Moderate thickness of SiC interphase in fiber bundles could increase the density of the composite, but when the thickness of SiC interphase was over 0.5 μm, more close pores formed and the density of the composite decreased. The SiC interphase could protect carbon fiber effectively from carbo-thermal reduction, but could not enhance the mechanical properties of C/ZrC composite. The flexural strength and fracture toughness of C/ZrC composites with 0.05 μm thickness SiC layer were 252 MPa and 13.6 MPa m^1/2, and for those with 0.5 μm thickness SiC layer 240 MPa and 12.8 MPa m^1/2, both close to the value of the composite without SiC interphase (254 MPa and 14.5 MPa m^1/2), while those with 0.7 μm thickness SiC layer were only 191 MPa and 10.8 MPa m^1/2, respectively. Moderate content of SiC interphase could improve the ablation property of C/ZrC composites; however excessive content of SiC interphase would decrease the ablation property.     

Investigation on microstructure and properties of dissimilar joint between SA553 and SUS304 made by laser welding with filler wire

The dissimilar joints between SA553 and SUS304 were produced by CO₂ laser welding with the ERNiMo-8 and ER308L filler wire. After welding parameters were optimized, qualified weld formations were made. Investigation on the microstructure showed that there were dual phases (martensite and austenite) in the ER308L weld, but only austenite in the ERNiMo-8 weld. For both joints, not only the microstructure gradient, but also the element gradient was observed near interfaces between weld metals and base metals. The Charpy impact and tensile test at room (25 °C) and low temperature (− 196 °C) was implemented. The cryogenic impact energy of the ER308L weldment was 51 J, lower than the value (84 J) of the ERNiMo-8 weldment. The corresponding cryogenic tensile strength of the two weldments was 1070 MPa and 960 MPa, respectively. The cryogenic tensile properties of both weldments were rather higher than requirements in the relevant standards. The ERNiMo-8 weldment showed relatively better comprehensive performance when the cryogenic toughness was considered.     

Dynamic fracture of bovine bone

True clinical fracture of bones in bovine, race horses or humans occur predominantly during impact loading (e.g. car accidents, falls or physical violence). Although static fracture tests provide an estimate of fracture toughness or R-curve behavior in bones, the static toughness values may be ill suited for predicting failure under dynamic loading conditions due to the visco-elastic response of bone (i.e. strain rate dependent properties). Despite decades of the study on deformation rate dependency of bone properties such as compression and fracture toughness, high-quality dynamic fracture data remain limited. Preliminary tests (compression and fracture toughness) have been conducted on dry and wet bovine bone under both static and dynamic loading conditions. While compression tests have been conducted with loading direction parallel and perpendicular to the bone axis (longitudinal and transverse, respectively), fracture tests were performed only in the transverse direction. The strain rate in compression tests varied between 10^− 3 and 10³ s^− 1, and the stress intensity rate varied between ∼10^− 3 and 10⁵ MPa√m/s. While low strain rate tests were conducted on conventional mechanical testing machines, high strain rate experiments were conducted on a split-Hopkinson bar under compression and a novel three-point bend configuration. The fracture morphology and the extent of damage of bone in each case were characterized using SEM, and an attempt is made to relate these to the rate dependent fracture toughness of the bone. It is believed that such understanding is crucial for mechanistic interpretation of bone fracture phenomenon and eventually for predicting bone failure reliably.