Effect of the composition and porosity of sintered titanium nanolaminates on their mechanical properties at high temperatures

By the methods of micro-and macroindentation, uniaxial compression, and scanning electron microscopy, we study the behavior of the structure and mechanical properties of mono-and biphase Ti₃SiC₂, Ti₃AlC₂, and Ti₄AlN₃ titanium nanolaminates (in-situ composites) prepared by the method of reaction sintering in compact and porous states. The regularities, specific features, and mechanisms of deformation and fracture processes are established for each material within the temperature range 20–1300°C. The temperature-strain and force boundaries of their existence in the plastic state are determined. The comparative analysis of the mechanical properties of nanolaminates is performed. It is shown that the strength characteristics of nanolaminates and their strain and creep resistance at medium and high temperatures increase in the following sequence: Ti₃AlC₂-Ti₄AlN₃-Ti₃SiC₂. The obtained picture of high-temperature properties of these materials is explained. It is shown that the procedure of prestraining of a porous material by ε = 4–8% may result in a significant increase in its specific high-temperature strength up to values higher than those typical of the compact material. __________ Translated from Problemy Prochnosti, No. 6, pp. 79–94, November–December, 2006.     

Compressional characteristics of native and pregelatinized forms of sorghum,plantain, and corn starches and the mechanical properties of their tablets

A study was made of the compressional characteristics of native and pregelatinized forms of sorghum, plantain, and corn starches and the mechanical properties of their tablets. Compressional characteristics were analyzed using density measurements and the Heckel and Kawakita plots. Pregelatinized starches exhibited more densification than native starches during die filling and at low pressures. The ranking for the mean yield pressure (Py) values for the starches was plantain < corn < sorghum, with the pregelatinized starches having lower values than the native starches. The ranking for the values of another pressure term, Pk--an inverse measure of plasticity, was corn < plantain < sorghum, but with the native starches having the lower values. For the tablets, the ranking for values of tensile strength (T) was corn > plantain > sorghum, while the ranking for the brittle fracture index (BFI) was plantain > corn > sorghum. Tablets made from pregelatinized starches had lower T and BFI values than those made from native starches. The results suggest that pregelatinization of the starches facilitated faster onset of plastic deformation but reduced the amount of plastic deformation which occurred during the compression process.     

The effect of silicon dioxide content of natural stones on their strength properties,material removal rate and power consumption in diamond grinding

The paper addresses the influence of silicon dioxide content of natural stones on their Mohs hardness, ultimate uniaxial compression strength, microhardness as well as on the removal rate and power consumption in diamond grinding of these materials. An increase in the amount of this constituent in natural stones is demonstrated to have an effect on strength properties and power consumption in grinding and a considerable effect on removal rate in diamond grinding.     

Microstructure and mechanical properties of a rapid solidified boron- modified duplex stainless steel

Two duplex stainless steels 2205 and 2205 with 2.5?wt-% B addition prepared by a fast solidification technique were investigated. The samples were arc melted and cast in a cylindrical mould with varying diameters in a single cavity that provided different cooling rates. The hardness increased in both cases for smaller diameters, however, there was a different profile from the surface to the centre in case of 2205 with 2.5?wt-% B. The microstructural investigation indicated that boron addition led to the formation of hard borides and grain refinement. Different boride morphologies that varied with the cooling rates were identified. The compression strength at room temperature improved by a factor of 3.5 with boron addition without considerably decreasing the ductility.     

Influence of granulating method on physical and mechanical properties, compression behavior, and compactibility of lactose and microcrystalline cellulose granules

The physical and mechanical properties of lactose (LC) and microcrystalline cellulose (MCC) granules prepared by various granulating methods were determined, and their effects on the compression and strength of the tablets were examined. From the force-displacement curve obtained in a crushing test on a single granule, all LC granules appeared brittle, and MCC granules were somewhat plastically deformable. Intergranular porosity ε_inter clearly decreased with greater spherical granule shape for both materials. Decrease in intragranular porosity ε_intra enhanced the crushing force of a single granule F_g. Agitating granulation brought about the most compactness and hardness of granules. In granule compression tests, the initial slope of Heckel plots K₁ appeared closely related to ease of filling voids in a granule bed by the slippage or rolling of granules. The reciprocal of the slope in the succeeding step 1/K₂ in compression of MCC granules indicated positive correlation to F_g, while in LC granules, no such obvious relation was evident. 1/K₂ differed only slightly among granulating methods. Tensile strength of tablets T_t obtained by compression of various LC granules was low as a whole and was little influenced by granulating method. For MCC granules, which are plastically deformable, tablet strength greatly depended on granulation. Granules prepared by extruding or dry granulation gave strong tablets. Tablets prepared from granules made by the agitating method showed particularly low T_t. From stereomicroscopic observation, the contact area between granule particles in a tablet appeared smaller; this would explain the decrease in intergranular bond formation.     

Biomineralization,antibacterial activity and mechanical properties of biowaste derived diopside nanopowders

This work reports on the preparation and characterization of mesoporous nano diopside (CaMgSi₂O₆) using a simple and cost-effective sol-gel combustion route. Stoichiometric oxidant/fuel ratio was adopted for the combustion reaction. Eggshell was used as a calcium source, glycine (fuel) as reductant, magnesium nitrate and nitric acid as oxidant were used in the preparation. The thermal behavior of the precursor was studied by thermo-gravimetric analysis (TGA) and heating microscopy. The temperature required for the transformation of the precursor into pure diopside was optimized at 1100 °C. Rietveld refinement method was utilized to confirm the phase purity of diopside. The resultant powder contains 36 nm particle with a specific surface area of 51 m²/g. The appearance of Ca, Mg, Si, and O peaks in EDX pattern confirmed the existence of essential elements. The rapid consumption of calcium and phosphorus ions from the simulated body fluid during dissolution indicated their involvement in apatite deposition on the surface of the nano diopside. FT-IR spectra showed that the SiO and SiOSi groups were replaced by phosphate bands due to hydroxyapatite deposition. The mechanical stability of the diopside after bioactivity studies was found to be superior to the cancellous bone. The release of alkaline earth ions (Ca²⁺ and Mg²⁺) from the diopside sample into the bacterial culture medium increases the pH (7.4), which inhibits the bacterial growth. The surface properties, concentration, and type of bacteria are the other factors responsible for the antibacterial activity of the nano diopside.     

Fe61Co10Zr5W4B20块体非晶合金的形成及其力学性能

采用铜模吸铸法获得直径为2 mm的Fe61Co10Zr5W4B20块体非晶合金.采用X射线衍射、扫描电镜、示差扫描量热仪、微显硬度及压缩实验等研究了非晶合金的结构、热稳定性、显微硬度与压缩性能.结果表明:Mo的引入不利于非晶合金的形成;Fe61Co10Zr5W4B20块体非晶合金表现为二级晶化,玻璃转变温度为561.1℃,晶化起始温度为619.0℃,第一晶化峰值温度为632.6℃,第二晶化峰值温度为747.0℃,过冷液相区为57.9℃;该非晶合金的显微硬度为1207HV0.2,抗压强度σbc为1707.6 MPa.     

Microstructure,mechanical properties and strengthening mechanisms of 5Cr5MoV modified by aluminum

The influence of aluminum on the microstructure and tensile properties of 5Cr5MoV was systematically investigated for improving the mechanical properties at room temperature. Microstructure was characterized by optical microscope (OM), scanning electron microscopy (SEM), field-emission transmission electron microscopy (FE-TEM), and additionally the uniaxial tensile tests were performed on a MTS-810 testing system. Tensile strength as a function of aluminum concentration exhibits an obvious two-stage characteristic. In stage I, 5Cr5MoV is continuously strengthened with the increase of aluminum, mainly owing to the refinement of lath martensite, the precipitation of small carbides and the presence of fine twins in martensite. The maximum tensile strength is 1303 MPa at the aluminum concentration of 1.63 wt.%. In stage II, the tensile strength rapidly drops down with the excessive addition of aluminum due to both the presence of large carbides at the boundaries between ferrite and martensite and the excessive ductile phase of irregular ferrites. As a result, the appropriate addition of aluminum can improve the mechanical properties of 5Cr5MoV by introducing the cryptocrystalline martensite as well as the dispersive polygonal ferrite in the microstructure.     

Preparation,characterization, and mechanical properties of polyacrylonitrile (PAN)/graphene oxide (GO) nanofibers

Abstract

Mostly, water filters are designed based on the steady state conditions “Laminar flow”, while the actual case is a turbulent flow as a result of chaotic changes in pressure and flow velocity, which can be lead to rapid failure thus decrease its service time. Also, the surface roughness of the synthesized filter was neglected, which has been classified as the main cause of shear failure. In this work, Polyacrylonitrile (PAN) nanofibers were enhanced by graphene oxide (GO) with different fractions in order to increase its performance, in terms of mechanical behavior. At the same time, GO was employed as a surface refining of the synthesized filter in order to decrease the friction between flow and filter surface thus delays the occurrence of shear failure. In this work, PAN/GO composite nanofibers were fabricated by electrospinning process. Different volume concentration of GO (0.05, 0.5, 1, and 1.5?wt%) have been investigated. PAN/GO composite nanofibers were characterized with scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). As demonstrated by the results of tensile testing, mechanical properties of PAN can be effectively enhanced with the addition of GO filler. At 1?wt% of GO filler nanofibers membranes achieved 64.4% rise of tensile strength and 71.4% improvement of Young’s modulus.     

Water absorption behavior,mechanical and thermal properties of nano TiO2 enhanced glass fiber reinforced polymer composites

Nano TiO₂ particle is one of the promising inorganic nano fillers used in polymer matrix composites to enhance the mechanical properties. However, reliability of this type of nano composites is yet to be ensured in hydrothermal environment. The present work investigates the addition of nano TiO₂ filler on water sorption, residual strength and thermal properties of glass fiber reinforced polymer (GFRP) composites. The results revealed that addition of 0.1 wt% TiO₂ has reduced water diffusion coefficient by 9%, improved residual flexural strength by 19% and residual interlaminar shear strength by 18% among all the nano TiO₂ modified composites. The improvement of mechanical properties in hydrothermal environment creates opportunity and reliability to be used in different engineering applications. Weibull design parameters are evaluated and found a good agreement between Weibull stress-strain curves and experimental one. Fractographic analysis confirmed the various failures and strengthening mechanisms of nano composites in dry and hydrothermal environment.     

Performance of ground clay brick in ASR-affected concrete: Effects on expansion, mechanical properties and ASR gel chemistry

The effects of ground clay brick (GCB) on alkali-silica reaction (ASR) expansion as well as on mechanical properties of ASR-affected concrete are investigated. Crushed red clay brick originated from demolished masonry was ground in a laboratory ball mill and replaced for portland cement at levels of 15% and 25% by weight in concrete mixes produced with alkali reactive sand. ASR expansion, compressive strength, flexural strength, and modulus of elasticity of the concrete mixes were evaluated. Effect of GCB on ASR gel chemistry was also studied on Pyrex glass-paste specimens using SEM/EDS (scanning electron microscope equipped with energy dispersive X-ray spectroscopy). The results indicate that GCB effectively reduces ASR expansion in concrete: associated cracking and loss on mechanical properties are also significantly reduced. SEM study suggests that GCB alters alkali silica gel chemistry thus resulting in a less expansive product.     

Effect of fibre characteristics on physical,mechanical and microstructural properties of geopolymer concrete: A comparative experimental investigation

The main aim of this work is to comparatively reveal the effect of fibre type, length and content on compressive strength and microstructure of structural geopolymer concrete (GPC) produced under constant mixture and curing parameters in order to address the significant gap in present literature. Firstly, GPCs with different NaOH concentrations (i.e., 6, 9, 12 and 15 M) and activator solution/binder (a/b) ratios (i.e., 0.45 and 0.55) were produced in ambient curing condition, and optimum production parameters were determined based on the preliminary evaluations. Then, glass and polypropylene fibres in 6-mm length (GS6 and PP6) and polyamide and polypropylene fibres in 12-mm length (PY12 and PP12) were included in GPCs at ratio of 0.4%, 0.8% and 1.2% (by volume). Compressive strength, apparent porosity, bulk density, ultrasonic pulse velocity (UPV), X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis of GPC samples were carried out comparatively. The inclusion of GS6 fibre enhanced the compressive strength thanks to fibre surface being covered by geopolymer gel and the strong adhesion between GS fibre and geopolymer matrix. SEM images of fibre reinforced GPC (FRGPC) also confirmed the experimental findings, which were attributed to improvement in compressive strength. Regardless of the fibre type, the maximum compressive value strength was obtained from GPC specimens with 0.4% fibre and then decreased. Higher fibre inclusions led to poor compaction, workability issues and inhomogeneous fibre dispersions. A very good relation (R² = 0.98) was acquired between UPV and compressive strength values of GPC/FRGPC samples.     

Microstructure, mechanical properties and chemical degradation of brazed AISI 316 stainless steel/alumina systems

The main aims of the present study are simultaneously to relate the brazing parameters with: (i) the correspondent interfacial microstructure, (ii) the resultant mechanical properties and (iii) the electrochemical degradation behaviour of AISI 316 stainless steel/alumina brazed joints. Filler metals on such as Ag–26.5Cu–3Ti and Ag–34.5Cu–1.5Ti were used to produce the joints. Three different brazing temperatures (850, 900 and 950 °C), keeping a constant holding time of 20 min, were tested. The objective was to understand the influence of the brazing temperature on the final microstructure and properties of the joints. The mechanical properties of the metal/ceramic (M/C) joints were assessed from bond strength tests carried out using a shear solicitation loading scheme. The fracture surfaces were studied both morphologically and structurally using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD). The degradation behaviour of the M/C joints was assessed by means of electrochemical techniques.

It was found that using a Ag–26.5Cu–3Ti brazing alloy and a brazing temperature of 850 °C, produces the best results in terms of bond strength, 234 ± 18 MPa. The mechanical properties obtained could be explained on the basis of the different compounds identified on the fracture surfaces by XRD. On the other hand, the use of the Ag–34.5Cu–1.5Ti brazing alloy and a brazing temperature of 850 °C produces the best results in terms of corrosion rates (lower corrosion current density), 0.76 ± 0.21 μA cm⁻². Nevertheless, the joints produced at 850 °C using a Ag–26.5Cu–3Ti brazing alloy present the best compromise between mechanical properties and degradation behaviour, 234 ± 18 MPa and 1.26 ± 0.58 μA cm⁻², respectively. The role of Ti diffusion is fundamental in terms of the final value achieved for the M/C bond strength. On the contrary, the Ag and Cu distribution along the brazed interface seem to play the most relevant role in the metal/ceramic joints electrochemical performance.     

Metakaolin-based inorganic polymer composite: Effects of fine aggregate composition and structure on porosity evolution,microstructure and mechanical properties

This paper examines the phase transformation, pore evolution, microstructural and mechanical changes that occur in inorganic polymer cement (IPC) in the presence of three different grade of fine aggregates (ф < 100 μm) of ladle slag, nepheline syenite and quartz sand. Experimental results indicate that polycondensation was enhanced in nepheline syenite based specimens, compared to quartz sand, due to the increase in HMAS phases in relation to the dissolution and interaction of amorphous/disordered fraction of aggregates. HCS and HCAS with HMAS phases were identified in the ladle slag based specimens. The formation of these new phases reduced both the cumulative pore volume and pores size. The apparent increase in volume of capillary pores in ladle slag based specimens was explained by the residual bubbles from the carbonates included in raw slag. The flexural strength of the inorganic polymer cement increases from 4 MPa to 4.2, 4.8 and 6.8 MPa with the addition of 20 wt% of quartz sand, nepheline syenite and ladle slag respectively. These values increase significantly between 28 and 180 days of curing (9.1 MPa for ladle slag and 10.0 MPa for nepheline syenite). It was concluded that fines can be used to remove the HM and poorly bounded alumina oligomers in metakaolin based inorganic polymer matrices and improve the interfacial zone for the design of an optimum grade and high-performance composites.     

Comparison of the mechanical and physical properties of a carbon fibre epoxy composite manufactured by resin transfer moulding using conventional and microwave heating

Microwave processing holds great potential for improving current composite manufacturing techniques, substantially reducing cure cycle times, energy requirements and operational costs. In this paper, microwave heating was incorporated into the resin transfer moulding technique. Through the use of microwave heating, a 50% cure cycle time reduction was achieved. The mechanical and physical properties of the produced carbon fibre/epoxy composites were compared to those manufactured by conventional resin transfer moulding. Mechanical testing showed similar values of flexural moduli and flexural strength for the two types of composites after normalisation of the corresponding data to a common fibre volume fraction. A 9% increase of the interlaminar shear strength (ILSS) was observed for the microwave cured composites. This enhancement in ILSS is attributed to a lowering of resin viscosity in the initial stage of the curing process, which was also confirmed via scanning electron microscopy by means of improved fibre wetting and less fibre pull-out. Furthermore, both types of composites yielded minimal void content (<2%). Dynamic mechanical thermal analysis revealed comparable glass transition temperatures for composites produced by both methods. A 15 °C shift in the position of the β-transition peak was observed between thermally and microwave cured composites, suggesting an alteration in the cross-linking path followed.     

Cold spray additive manufacturing of Invar 36 alloy: microstructure,thermal expansion and mechanical properties

In this work,the Invar 36 alloys were manufactured using cold spray (CS) additive manufacturing technique.The systematic investigations were made on the microstructural evolution,thermal expansion and mechanical properties under as-sprayed (AS) and heat-treated (HT) conditions.XRD (X-ray diffraction)and ICP-AES (inductively coupled plasma atomic emission spectroscopy) analyses show that no phase transformation,oxidation,nor element content change have occurred.The X-ray computed tomography (XCT) exhibited a near fully dense structure with a porosity of 0.025％ in the helium-produced sample under as-sprayed condition,whereas the nitrogen-produced samples produced at 5 MPa and 800 ℃ show more irregular pore defects.He-AS sample shows a more prominent grain refinement than that of nitrogen samples due to the more extensive plastic deformation.The post heat-treatment exhibited a promoted grain growth,inter-particle diffusion,as well as the formation of annealing twins.Between 25 ℃ and 200 ℃,the nitrogen samples possessed lower CTE (coefficient of thermal expansion) values (1.53 × 10-6/℃) compared with those produced by casting and laser additive manufacturing.The He-AS samples exhibited a noticeable negative CTE value between 25 ℃ and 200 ℃,which may due to the significant compressive residual stress (-272 MPa) compensating its displacement with temperature increase during CTE test.The N2-HT and He-HT Invar 36 samples present a notable balance between strength and ductility.In conclusion,the CS technique can be considered as a potential method to produce the Invar 36 component with high thermal and mechanical performance.     

Study on dislocation density,microstructure, and mechanical properties of P92 steel for different heat treatment conditions

The impact of various heat treatment procedures on microstructure, dislocation density, hardness, tensile characteristics, and impact toughness of P92 steel was examined in the current experiment. The martensitic microstructure and average microhardness of 463 HV 0.2±8 HV 0.2 of the normalized steel were prevalent. A tempering procedure was carried out at 760 °C for a range of 2 hours to 6 hours. Additionally, an X-ray diffraction examination was carried out, and the results were used to determine the dislocation density. The normalized sample was characterized by a high dislocation density. The dislocation density was decreased by tempering of normalized samples. With an increase in tempering time, the effect of the treatment coarsened the grains, precipitates, and decreased the area fraction of precipitates. After tempering, MX, M₂₃C₆, and M₇C₃ types precipitates were found to have precipitated, according to energy dispersive spectroscopy and x-ray diffraction research. The ideal tempering period was determined to be 4 hours at a tempering temperature of 760 °C based on the microstructure and mechanical characteristics. Steel that was tempered at 760 °C for 4 hours had a yield strength of 472 MPa, an ultimate tensile strength of 668.02 MPa, and an elongation of 26.05 %, respectively.     

Effect of thermal annealing on the microstructure,mechanical properties and residual stress relaxation of pure titanium after deep rolling treatment

The aim of this paper was to investigate the effect of thermal annealing on the microstructure, mechanical properties, and residual stress relaxation of deep rolled pure titanium. The microstructure and mechanical properties of the surface modified layer were analyzed by metallographic microscopy, transmission electron microscope and in-situ tensile testing. The results showed that the annealed near-surface layer with fine recrystallized grains had increased ductility but decreased strength after annealing below the recrystallization temperature, where the tensile strength was still higher than that of the substrate. After annealing at the recrystallization temperature, the recrystallized near-surface layer had smaller grain size, similar tensile strength, and higher proportional limit, comparable to those of the substrate. Moreover, the residual stress relaxation showed evidently different mechanisms at three different temperature regions: low temperature (T?≤?0.2?T_m), medium temperature (T?≈?(0.2?0.3)?T_m), and high temperature (T?≥?0.3?T_m). Furthermore, a prediction model was proposed in terms of modification of Zener-Wert-Avrami model, which showed promise in characterizing the residual stress relaxation in commercial pure Ti during deep rolling at elevated temperature.     

Comparison of the thermal,dynamic mechanical and morphological properties of PLA-Lignin & PLA-Tannin particulate green composites

The study of Lignin and Tannin as filler materials in PLA-based polymeric systems has been uncommon in literature. Composites of PLA-Lignin with 5, 10, 15 wt% Lignin and PLA-Tannin with 5, 10, 15 wt% Tannin were fabricated using injection moulding. SEM morphology reveals Lignin forms droplet like dispersions within the PLA matrix in contrast to Tannin. The particle size of Lignin within the matrix is also 10–150 times smaller than Tannin. Isothermal frequency sweeps on the composites show that storage modulus of PLA-Tannin composites starts to degrade at 15 wt% filler concentration and damping rises. PLA-Lignin composites do not show such degradation in storage modulus. The tensile strength of both PLA-Lignin and PLA-Tannin composites falls with increase in filler content. Lignin has a more inhibitory effect on PLA crystallization than Tannin. The onset of thermal degradation of PLA-Lignin and PLA-Tannin composites occurs at slightly lower temperatures than pure PLA.     

Fresh and mechanical properties,and strain sensing of nanomodified cement mortars: The effects of MWCNT aspect ratio,density and functionalization

A comprehensive analysis on the effect of aspect ratio, bulk density and functionalization of multi walled carbon nanotubes (MWCNTs) in the development of nanomodified mortars, reinforced with different types of MWCNTs is presented herein. A structural characterization of the pristine and functionalized carbon nanotubes was carried out with scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). A simple one step dispersion method, involving the application of ultrasonic energy and the use of a superplasticizer (SP) was utilized for the preparation of uniformly dispersed MWCNT suspensions. The experimental determination of the fresh and 28d mechanical properties of mortars with w/c = 0.5 and s/c = 3.0, using four different types of well dispersed pristine and functionalized MWCNTs at an amount of 0.1 wt% of cement took place through: (i) flow and time of setting tests; (ii) three point bending experiments on 4 × 4 × 16 cm specimens; and (iii) uniaxial compression on the half prisms of the flexural test specimens (4 × 4 × 8 cm). The piezoresistive behavior of the mortars reinforced with the pristine MWCNTs was experimentally determined using the 4-pole method, and compared with the strain sensing ability of the mortars reinforced with the functionalized MWCNTs. All MWCNT reinforced mortars exhibit a remarkable enhancement in the mechanical properties. However, the 28d flexural strength, young's modulus and energy absorption capability of the mortars reinforced with the mechanically functionalized MWCNTs at an amount of 0.1 wt% increased by 120%, 124%, and 103% respectively. Finally, depending on the procedure of the functionalization, chemical or mechanical, a different effect on the intrinsic properties of MWCNTs was observed. The carboxylic groups attached to the surface of the chemically functionalized MWCNTs indeed provided them with the ability of a uniform and effective dispersion, without the need of a sonication procedure. On the other hand, it was found that functionalized MWCNTs do not always retain the electrical properties of pristine MWCNTs.