Elastic Recovery Index Research Articles

Assessment of microstructure, nanomechanical and tribological properties of Ti-xNi alloys fabricated by spark plasma sintering

This work employed the nanoindentation and conventional dry sliding wear techniques to study the nanomechanical and tribological properties of the spark plasma sintered Ti-xNi (x = 2, 6 and 10 wt%) alloys. The microstructure and phase composition of the fabricated alloys were studied. The results indicated the presence of hexagonal close-packed (hcp) α-Ti and face-centred cubic (fcc) Ti2Ni intermetallic phases within the matrix of the Ti-xNi alloys. Nanoindentation measurements under varying loads showed that the hardness (H), elastic modulus (Er) and elastic recovery index (We/Wt) of the developed alloys increased with increasing nickel contents. At a constant load, the hardness trend aligns perfectly with the indentation size effect phenomenon. The H and Er decreased upon transition from lower to higher loads. The H/Er and H3/Er2 ratios obtained from nanoindentation are higher for Ti-xNi alloys compared to pure Ti. This shows that the Ti-xNi alloys possessed better anti-wear characteristics than pure Ti. The wear analysis results show that the wear resistance increased with increasing volume fraction of the Ti2Ni intermetallics in the sintered samples. Ti–10Ni alloy displayed the best nanomechanical and wear performances among the sintered samples.

Nanoindentation and Structural Analysis of Sintered TiAl(100-x)-xTaN Composites at Room Temperature.

The nanohardness, elastic modulus, anti-wear, and deformability characteristics of TiAl(100-x)-xTaN composites containing 0, 2, 4, 6, 8, and 10 wt.% of TaN were investigated via nanoindentation technique in the present study. The TiAl(100-x)-xTaN composites were successfully fabricated via the spark plasma sintering technique (SPS). The microstructure and phase formation of the TiAl sample constitute a duplex structure of γ and lamellar colonies, and TiAl2, α-Ti, and TiAl phases, respectively. The addition of TaN results in a complex phase formation and pseudo duplex structure. The depth-sensing indentation evaluation of properties was carried out at an ambient temperature through a Berkovich indenter at a prescribed load of 100 mN and a holding time of 10 s. The nanoindentation result showed that the nanohardness and elastic modulus characteristics increased as the TaN addition increased but exhibited a slight drop when the reinforcement was beyond 8 wt.%. At increasing TaN addition, the yield strain (HEr), yield pressure (H3Er2), and elastic recovery index (WeWt) increased, while the plasticity index (WpWt) and the ratio of plastic and elastic work (RPE) reduced. The best mechanical properties were attained at the 8 wt.%TaN addition.

Heterogeneous microstructure in nonequiatomic MoNbTaVW refractory high entropy alloy after high pressure torsion: Evolution mechanisms and mechanical properties

The non-equiatomic MoNbTaVW refractory high entropy alloy (HEA) has been systematically investigated with the intent of developing a heterogeneous microstructure using high pressure torsion (HPT). The heterogeneous microstructure is successfully developed and is characterized by coarse grains, kink bands and ultrafine grains (UFGs) at strain levels (ε) ≈ 0–2.4, 2.4–6.2, and 8.7-higher, respectively. In the initial stage (ε ≈ 2.4–6.2) of deformation, the microbands (slip bands and kink bands) developed within the grain depending on the orientation. The slip bands are developed by slip activity along {110} <11‾1 > slip system, and kink bands are formed due to slip-induced lattice rotation about the <110> axis with activation of {112}<111‾ > slip system. At higher strain (ε > 8.7), high density of accumulated low angle grain boundaries (LAGBs) dynamically recovered into polygonized subgrain structures that later transform into high angle grain boundaries (HAGBs) due to gradual lattice rotation. The synchrotron diffraction pattern confirms that the single-phase bcc structure is stable during the deformation, and no phase transformation takes place. Further, the microhardness values for coarse grained, kink banded and UFG microstructure are determined to be 8.1, 10.3, and 12.5 GPa, respectively. The mechanical behaviour of the HPT microstructure indicates that the UFG have a good impact resistance and elastic recovery index, while the coarse grains has inherent plasticity and better fracture resistance. The kink band microstructure remarkably combines strong impact loading and inherent plasticity. Therefore, the hierarchical distribution of these microstructures can achieve a superior combination of strength and ductility

Nanoindentation study of mechanical and wear properties of spark plasma sintered Ti-6Ni-xTiCN composites

In this study, monolithic pure Ti and Ti-6Ni-xTiCN composites were fabricated by the spark plasma sintering method and the mechanical and anti-wear characteristics of the fabricated samples were investigated using the nanoindentation technique. Microstructural and phase analysis of the sintered samples showed the predominance of the α-Ti phase in the unreinforced pure Ti matrix. In addition to the α-Ti phase, in-situ TiN, Ti2Ni intermetallic, and undissolved TiCN phases were detected in the matrix of the composites. Nanoindentation results revealed that the hardness (H), elastic modulus (Er) and elastic recovery index (We/Wt) of the investigated samples increase with increasing reinforcement contents under varying loads of 50 mN, 100 mN and 150 mN. The nanomechanical and anti-wear properties of the analysed samples indicated dependency on the applied indentation load. The Ti-6Ni-xTiCN composites displayed higher H/Er,H3/Er2 and We/Wt ratios that signified better wear and impact resistance than the unreinforced pure Ti. Microstructural integrity, which ensures consistency between the anti-wear characteristics obtained through the nanoindentation technique and the conventional wear testing, was achieved in composites containing TiCN nanoceramic contents up to 10 wt%. Ti-6Ni-10TiCN composite displayed the optimum combination of the nanomechanical and anti-wear properties across the applied loads.

Nondestructive measurement of the mechanical properties of graphene nanoplatelets reinforced nickel aluminium bronze composites

Nanoindentation is a viable method to assess the mechanical properties of developed alloys and composites at the nanometer scale without hampering the microstructure and integrity of materials. In this study, nondestructive measurement was conducted on spark plasma sintered nickel aluminium bronze (NAB), and graphene nanoplatelets (1, 2, 3 wt.%) reinforced NAB composites using the nanoindentation technique. The nondestructive measurements were conducted under loads of 50 mN and 100 mN to assess the nanohardness and reduced elastic modulus of the fabricated NAB alloy and composites. Further investigations were carried to evaluate the elastic recovery index, plasticity index, the nanohardness and reduced modulus ratio, and the yield pressure to reveal the nanomechanical responses of the fabricated materials. Scanning electron microscopy was used to analyze and reveal the dispersibility of the graphene nanoplatelets (GNP) in the NAB matrix. The nondestructive measurements showed that the nanohardness, reduced elastic modulus, yield pressure, resistance to elastic strain to failure and the elastic recovery index improved with the presence and increase in the concentration of GNP in the NAB matrix. The reduced elastic modulus and nanohardness values range from 34.2 – 43.0 GPa and 4407.2–6598.8 MPa respectively, which declined with nanoindentation loads. The fabricated NAB alloy experienced the maximum plastic deformation and least resistance to impact loading.

Nanoindentation studies and analysis of the mechanical properties of Ti-Nb2O5 based composites

In this study, nanoindentation tests were used to evaluate the mechanical properties of spark plasma sintered Ti based composites containing 5, 10 and 15 wt.% Nb2O5, targeted for potential use as biomedical material. Nanoindentation tests were performed on the samples using indenter loads of 20 and 100 mN, while the microstructures were characterized using scanning electron microscopy. It was noted that with increasing Nb2O5 wt.%, there is transition from the lamellar structure of pure Ti to fully bimodal structures for the Ti-10 wt.% Nb2O5 and Ti-15 wt.% Nb2O5 composites. The hardness (6.0–40.67 GPa (20 mN) and 2.4–12.03 GPa (100 mN)) and reduced elastic modulus (115–266.91 GPa (20 mN) and (28.05–96.873 GPa (100 mN)) of the composites increases with increase in the Nb2O5 content, attributed to contributions of load transfer from the Ti matrix to the relatively harder Nb2O5 particles, particle and dispersion strengthening mechanisms. The elastic recovery index also improved with increase in Nb2O5 content, while the inverse was noted with respect to plasticity index. The elastic strain to failure and yield pressure both improved with increase in Nb2O5 content, which suggests that the antiwear properties and resistance to impact loading equally improves with Nb2O5 addition.

Nanomechanical properties of spark plasma sintered multiwall carbon nanotubes reinforced Ti6Al4V nanocomposites via nanoindentation technique

In this study, nanoindentation tests were carried out to investigate the nanomechanical behaviours of Ti6Al4V and its nanocomposites comprising of multiwall carbon nanotubes (MWCNTs) fabricated via spark plasma sintering. Prior to the nanoindentation tests, the fabricated alloy and the nanocomposites comprising of 0.5 and 1.0 wt% of MWCNTs were observed under a scanning electron microscope (SEM) to reveal the morphology and the presence of the MWCNTs in the nanocomposites. The nanoindentation study was conducted using a Berkovich diamond indenter with a load of 75 mN to ascertain the nanohardness, reduced elastic modulus, plasticity index and elastic recovery index of the sintered materials. The SEM results revealed the dispersibility of the nanotubes in the titanium-based matrix and the presence of lamellar structures in the fabricated alloy. Furthermore, it was observed that the nanohardness and elastic modulus of the sintered materials ranges from 3.4–5.7 GPa and 27.6–38.9 GPa, which improved with the MWCNTs content. Also, the elastic recovery index increased with MWCNTs content in the nanocomposites. While the sintered Ti6Al4V displayed the maximum plasticity during the nanoindentation study.

Nanoindentation studies of the mechanical behaviours of spark plasma sintered multiwall carbon nanotubes reinforced Ti6Al4V nanocomposites

In this study, the influence of multiwall carbon nanotubes (MWCNT) additions on the mechanical properties of sintered Ti6Al4V-based nanocomposites was investigated. The nanocomposites were fabricated with varying weight fractions of MWCNT (0.5, 1.0 & 1.5 wt%) using the spark plasma sintering (SPS) technique. Investigations were carried out using nanoindentation of varying indentation loads (50 mN, 75 mN and 100 mN) to assess the nanohardness (H) and reduced elastic modulus (Er) of the alloy and nanocomposites. Further analysis was done to evaluate the elastic recovery index (WeWt), plasticity index (WpWt), elastic strain resistance (HEr) and yield pressure (H3Er2) at the maximum load. Microstructural analysis revealed the presence of the MWCNT dispersed across the alpha and beta phases of the Ti6Al4V matrix. The nanoindentation studies showed that the nanohardness, elastic modulus, elastic recovery index, elastic strain resistance and anti-wear properties improved with the MWCNT addition and continually increased with increase in nanotubes content. Also, it was observed that the nanohardness and reduced elastic modulus of the fabricated nanocomposites are in the range of 4677–9276 MPa and 29.3–60.9 GPa respectively which declined with increase in indentation load. The sintered Ti6Al4V displayed the least resistance to plastic deformation.

Recovery of scratch deformation formed on crosslinked polyorganosiloxane films

As consumers generally desire longer lasting scratch-free coatings, scratch resistance has become one of the most important properties of automotive coatings. Surface scratches that deform a coating but do not break it can recover over time, eventually even becoming invisible to the human eye. This phenomenon arises from elastic-plastic behavior and is called "self-recovery". This paper mainly focuses on the recovery of scratch deformations. Conventional coatings with low glass transition temperature (Tg) have fast recovery characteristics, like rubbers, but cannot attain sufficient hardness. Therefore, it is difficult to simultaneously improve both scratch recovery characteristics and hardness in conventional coatings such as 2 K urethane coatings consisting of acrylic polyols because both arise from the same causes as the mobility of the main chain of the coating. Herein, we explore the remarkable improvement of scratch recovery characteristics without sacrificing hardness by using a base resin with a siloxane main chain instead of a carbon-carbon main chain such as that of an acrylic polyol.We demonstrate that crosslinked polyorganosilsesquioxane coatings (Si-films) achieve both hardness suitable for automobile coatings and improved scratch recovery characteristics superior to those of conventional coatings (C-films). Si-films demonstrated 20% better elastic recovery index than C-films, and the Si-films recovered about twice as fast as the C-films. Scratch deformations on the Si-films almost disappeared after 15 min, even at room temperature, while C-films were needed over 24 days. Thus, coatings based on a siloxane main chain may offer dramatically improved self-recovery.

Study of compressibility properties of yogurt powder in order to prepare a complementary formulation.

The aim of the present study was to prepare an oral tablet from liquid yogurt by reforming the physical properties for easy transportation, long-term storage and also as a complementary dairy product in case of nutrient deficiency. The liquid fresh yogurt was lyophilized at -40°C and 0.03 mTor pressure. The dry powder was homogenized by a 12 mesh size sieve. Some tests such as Carr's compressibility index, Hausner ratio and the angle of repose were applied to evaluate the flowability of yogurt powder. Study of the deformation of particles during forcing was done by calculation of the elastic recovery index. Carr's compressibility index percent and Hausner ratio were calculated 15 and 0.94, respectively. The range of repose angle was measured between19-20°. The elastic recovery was obtained up to 60%. Since the hardness of tablets increased by decreasing compression velocity, therefore yogurt powder might have a plastic deformation. The reduction of powder volume due to compression force was about 20% (p < 0.05). Tablets with low fat yogurt showed very good compressibility with 6-12 Strong-Cab (SC) hardness units. Producing a complementary formulated as a tablet from yogurt powder is possible and also maybe therapeutically effective against lactose-intolerance syndrome and preventing antibiotic-associated diarrhea.We suggest that for more authentic confirmation of the type of deformation, it should go through Heckel's equation analysis, too.

Investigation of the physical–mechanical properties of Eudragit® RS PO/RL PO and their mixtures with common pharmaceutical excipients

Ammonio methacrylate copolymers Eudragit® RS PO and Eudragit® RL PO have found widespread use as key components in various types of extended release solid dosage forms. The deformation behavior of neat polymers and binary mixes was evaluated using Heckel Analysis, strain rate sensitivity, work of compaction and elastic recovery index. Additionally, the compact forming ability of neat materials and binary mixes were evaluated by analyzing their tabletability, compressibility and compactibility profiles. The Heckel analysis of both polymers exhibited a speed-sensitive deformation behavior typical to plastic materials. The yield values of the binary mixes of the polymers with microcrystalline cellulose revealed a linear relationship with the weight fractions of individual components. The yield values of binary mixes of both the polymers with dibasic calcium phosphate exhibited slight negative deviations from linearity. Both polymers exhibited axial relaxation after ejection typical of viscoelastic materials, as measured by the elastic recovery index values. The work of compaction and the elastic recovery index values of the binary mixtures were found to be linearly related to the weight fractions of the individual components thus, confirming ideal mixing behavior based on the composition. Addition of microcrystalline cellulose to both polymers significantly improved their tabletability and compactibility. The tensile strengths of the compacts prepared with neat materials and binary mixes with microcrystalline cellulose, dibasic calcium phosphate and lactose were the function of their solid fraction and independent of the tableting speeds tested; thus, validating compactibility as a reliable parameter in predicting acceptable tablet properties.

The use of an Elastic Recovery Index as a Criterion of Compactional Behaviour of Some Direct Compression Bases

AbstractThe effects of compression force and holding time on computer logged strain movements (at constant stress) and elasticviscoelastic expansions (on load release) of compacts made from eight pharmaceutical powders are reported. The feasibility of using an elastic recovery index (the ratio of elastic recovery to viscoelastic strain movements) to predict the quality of a material is also discussed.All compacts continued to consolidate by viscoelastic and plastic flow when held under constant stress during the holding period. The “compressible” bases Avicel PH-101 and Sta-Rx 1500 exhibited more time dependent movements than powders such as Paracetamol DC, Paracetamol, Emcompress and magnesium stearate. Poorly compressible materials such as magnesium carbonate and paracetamol showed the greatest elastic expansions on load release.It has been found that the elastic recovery indices of the compressible materials were lower than those of poorly compressible powders.