Mechanical Properties Of Individual Phases Research Articles

Compensating varying size effect in diamond cutting of SiCp/Al by ultrasonic elliptical vibration

The heterogeneous mechanical properties of individual phases in SiCp/Al result in significant varying size effect (SE) existed in its deformation process. And modulating the varying SE is crucial for improving the machined surface finish of SiCp/Al in mechanical machining. In this study, we elucidate the mechanisms governing the varying SE in conventional cutting and ultrasonic elliptical vibration-assisted cutting (UEVC) of SiCp/Al using diamond tools by theoretical analysis, numerical simulations and experiments. Specifically, the impact of cutting tool-workpiece contact states in UEVC on the fundamental cutting behavior of SiCp/Al, in terms of microscopic deformation modes and their correlations with machining force variation, machined surface morphology and chip profile, is evaluated. Subsequently, ultrasonic elliptical vibration-assisted diamond turning of SiCp/Al is performed to achieve a surface roughness of 20 nm accompanied with significantly suppressed tool wear. Finally, the compensation effect on the varying SE in SiCp/Al cutting by ultrasonic elliptical vibration of cutting tool is discovered, which leads to decreased brittle fracture and improved surface integrity. The research findings provide a theoretical support for understanding the machining mechanisms of UEVC of SiCp/Al, as well as proposing new perspectives for improving the machinability of SiCp/Al composite accompanied by suppressed varying SE.

Micromechanical properties of 4-year-old composite binder pastes with different mineral admixtures using nanoindentation technique

The elasticity modulus and hardness of various phases in 4-year-old Portland cement paste, cement paste containing fly ash, granulated blast furnace slag (BFS) or steel slag at low water/binder ratio were determined by the statistical nanoindentation technique. The influences of different mineral admixtures on mechanical properties of individual phases were comparatively analysed. The pores were not detected in cement paste containing mineral admixtures, which exhibit the extremely dense microstructure at 4 years. Most phases were HD C–S–H and UHD C–S–H in all 4-year-old pastes. The addition of different mineral admixtures does not affect the mechanical property of each phase but alters its volume fraction in cement paste. The incorporation of mineral admixtures reduces the volume fraction of LD C–S–H but remarkably increases the volume fraction of high stiffness C–S–H, especially UHD C–S–H. The total amount of C–S–H in 4-year-old cement paste containing BFS is the highest. The 4-year-old cement paste containing steel slag has the largest amount of high stiffness C–S–H. Increasing curing age increases the volume fraction of high stiffness C–S–H compared with reported data in the literature.

On the role of continuity in statistical nanoindentation of composite microstructures

AbstractThe validity of the statistical nanoindentation (SNI) technique for cementitious materials has been questioned by numerous researchers; however, it is still a commonly used method in literature. This study revisits assumptions pertaining to continuum mechanics of the method by using a well‐established selective SNI method to evaluate continuity in the mechanical response of each indent. Ordinary portland cement (OPC) was investigated alongside a two‐phase aluminosilicate ceramic (Al–Si). Filtering for continuity of indents eliminated a majority of indents in each sample. The indents meeting continuity requirements in the OPC sample had moduli values in the range of documented calcium silicate hydrates and portlandite—the predominant hydration phases in OPC. In the Al–Si sample, 73% of continuous indents were assigned to a mullite phase, although the chemical analysis showed only 42% mullite. This was attributed to the embedded morphology of the mullite phase, which made it more susceptible to structural compliance. These observations suggest that SNI may be ineffective for measuring the mechanical properties of individual phases in a microstructure if they are not prolific enough to exhibit a continuous indent response. Discontinuous indents due to microstructural interaction between phases were also shown to have a potential influence on the number of clusters (i.e., phases) suggested by the deconvolution algorithms.

Big Data Nanoindentation and Analytics Reveal the Multi-Staged, Progressively-Homogenized, Depth-Dependent Upscaling of Rocks’ Properties

This paper presents a newly observed phenomenon of upscaling of rocks’ properties using big data nanoindentation and analytics involving Gaussian mixture modeling (GMM), leading to characterizing the cross-scale mechanical properties of four shales and one sandstone. A large number (i.e., ~ 500) of statistical indentation measurements to depths of 6–8 μm were performed on each rock, resulting in continuous depth-dependent hardness and Young’s modulus data from unknown phases, which were then segmented at various depths to extract an array of discretized subdatasets. Two-dimensional GMM of each subdataset yields the number, fraction, and properties of mechanically distinct phases, and re-assembly of these results leads to clearly discernible property-depth curves. Such improved data analytics consisting of data segmentation, GMM deconvolution, and re-assembly enables the transformation of a massive number of chaotic curves from unknown phases into a few discernible lines corresponding to identified phases, from which the mechanical properties of individual phases are accurately determined at relatively small depths. With increasing depth, initially unique mechanical properties of individual phases undergo multistage merging at the intermediate mesoscale and progressively homogenize into a unified value at large depths or macroscale (e.g., > ~ 5 μm), which is regarded as the bulk rock’s properties. More importantly, such depth-dependent transition and progressive merging and homogenization actually manifest the micromechanics of nanoindentation on a heterogeneous composite, including the indentation surround effect and rock’s microstructure (e.g., sizes and spacings of different solid particles and their properties). Compared to different micromechanical upscaling models, this newly developed big data indentation technique and pertinent data analytics enable more accurate, multi-parameter, and cross-scale characterization of highly heterogeneous materials and explicitly uncover the multi-staged, progressively-homogenized, depth-dependent upscaling of elasticity from individual constituents at the nanoscale to merged virtual interface phases at the mesoscale and to bulk material at the macroscale.

Microstructural evolution and nanoindentation of NiCrMoAl alloy coating deposited by arc spraying

Arc spraying is a flexible thermal spray coating that can be used in on-site applications. In this study, a NiCrMoAl alloy was coated onto a mild steel substrate by arc spraying. The cored wire feedstock and the deposited coating were extensively characterized by a combination of X-ray diffraction, scanning electron microscopy, focused ion beam microscopy and transmission electron microscopy. Vickers microhardness and nanoindentation were used to investigate the mechanical properties of individual phases in the coating. The results showed that the NiCrMoAl alloy cored wire feedstock primarily consisted of material in elemental form including Ni, Cr, Mo, Al, Si, and Ti, whilst the arc sprayed coating contained a solute-lean γ-Ni phase, a (Mo, Si)-rich γ-Ni phase, elemental Mo splat as well as Cr2O3, Al2O3, and SiO2 at intersplat regions, together with ≤100 nm spherical Al2O3 particles within the splats. Partitioning of Mo and Si into the γ-Ni phase was observed following the rapid solidification of the splat on deposition. The Vickers hardness analysis showed that the average overall hardness of the coating was about 3.65 ± 0.56 GPa. However, nanoindentation indicated that the highest hardness was in the γ-Ni splat regions, especially those containing a high concentration of solute. The microstructural evolution, as well as the structure and chemistry of the phases that affect mechanical properties in the coating are discussed in detail.

Evaluation of Phase Transformation and Mechanical Properties of Metastable Yttria-Stabilized Zirconia by Nanoindentation.

Microscopical nonuniformity of mechanical properties caused by phase transformation is one of the main reasons for the failure of the materials in engineering applications. Accurate measurement of the mechanical properties of each phase is of virtual importance, in which the traditional approach like Vickers hardness cannot accomplish, due to the large testing range. In this study, nanoindentation is firstly used to analyze the mechanical properties of each phase and demonstrate the phase transformation in thermal barrier coatings during high-temperature aging. The distribution of T-prime metastable tetragonal phase, cubic and tetragonal phase is determined by mapping mode of nanoindentation and confirmed with X-ray diffraction and scanning electron microscope observation. The results show that during 1300 °C aging, the phase transition of metastable Yttria-Stabilized Zirconia induces the quick decrease of T′ phase content and an increase of T and C phases accordingly. It is found that there are some fluctuations in the mechanical properties of individual phase during annealing. The hardness and Young’s modulus of T′ increase at first 9 h, due to the precipitation of Y3+ lean T phase and then decrease to a constant value accompanied by the precipitation of Y3+ rich C phase. The relevant property of C phases also increases a little firstly and then decreases to a constant, due to the homogenization of Y3+ content, while the hardness and Young’s modulus of T phase remain unchanged. After aging of 24h the hardness of T′, C and T phases are 20.5 GPa, 21.3 GPa and 19.1 GPa, respectively. The Young’s modulus of T′, C and T phases are 274 GPa, 275 GPa and 265 GPa, respectively. Present work reveals the availability of nanoindentation method to demonstrate the phase transformation and measure mechanical properties of composites. It also provides an efficient application for single phase identification of ceramics.

Microscale fracture mechanisms of HfO2-Si environmental barrier coatings

Environmental barrier coatings (EBCs) play a vital role in protecting advanced turbine components subjected to extreme service environments, where mechanical, thermal and chemical behaviors typically dominate the design criteria. This study focuses on investigating the mechanical properties of individual phases within a HfO2-Si ceramic matrix composite (CMC) structure through implementation of notched microcantilevers and micropillar splitting experiments. The microcantilever experiments resulted in fracture toughnesses ranging between 1.38–1.52 MPa-m1/2 for the Si-rich phase and 2.26–2.38 MPa-m1/2 for the HfO2-rich phase depending on the method of analysis. From our micropillar splitting experiments, we found fracture toughnesses of 1.13 ± 0.39 MPa-m1/2 for the Si-rich phase and 1.18 ± 0.26 MPa-m1/2 for the HfO2-rich phase. Comparisons with bulk single edge V-notched beams (SEVNBs) suggest the micropillar results are accurate whereas the microcantilever experiments may overestimate KIC of the Si-rich and HfO2-rich phases by ˜0.2–1.2 MPa-m1/2, most likely, due to dimensional errors that affect specimen and model compliances.

Size Effects and Charting the Physical and Mechanical Properties of Individual Phases and Interphases in Polycrystalline Materials

Size effects in the hardness of individual phases and inclusions of multiphase materials are studied via micro- and nanoindentation for a number of rock samples (polycrystalline ferruginous quartzites, granite, anthracite, sandstone, marble, and verd antique). The distribution of the local physical and mechanical properties of the studied materials is charted. Size effects in hardness and correlations between the distribution of local physical and mechanical properties and the morphology of the studied samples are found.

Room temperature mechanical properties and microstructure of a low alloyed TRIP-assisted steel subjected to one-step and two-step quenching and partitioning process

The capability of one-step and two-step quenching and partitioning processes (Q&P) to treat the microstructure of a low alloyed TRIP-assisted steel was considered. The treated microstructures primarily consisted of lath martensite, retained austenite, lower bainite, and fresh martensite. Two various types of retained austenite in respect of size and morphologies were observed: blocky and film-like retained austenite. Short holding times were appropriate for carbon enrichment of the retained austenite. However, the volume fraction and carbon concentration of retained austenite vs. partitioning time followed an opposite trends in two step processed microstructures. This was attributed to the competitive processes of bainite or epsilon carbide formation at the specified partitioning temperature. The nano indentation experiments were employed to assess the local mechanical properties of individual phases specifically martensite and enriched retained austenite. The frequent pop-in in load-displacement curves indicated the capability of enriched austenite for martensitic transformation. Owning to the higher diffusion rate, the carbon concentration was relatively higher in two-step processed microstructures. In addition, film like or lamellar morphologies (which hold higher population in partitioned structures at 400 °C) possessed better transformation stability rather than a blocky type, which tends to transform to martensite under higher amount of strain. The evolution of mechanical properties was discussed relying on the variations of volume fraction, morphology and carbon concentration of retained austenite.

Microstructure and mechanical properties of titanium/steel bimetallic joints

In this paper, we report the investigation of Ti/Fe bimetallic plates welded with Cu-V filler. The microstructures and mechanical properties of individual phase were examined using combined microstructural analysis and nanoindentation test. Bending test was conducted to understand the overall mechanical behavior of the joint. The metallurgical reactions and evolution of phase composition during the welding process were discussed. It is interesting to note that the crack nucleation and propagation in different phases depend not only on the size and distribution of brittle intermetallics but the morphology of ductile phases.

Mechanical properties of individual phases of ZrB2-ZrC eutectic composite measured by nanoindentation

Zr-based ceramics are of interest for applications in aerospace propulsion, owing to their high hardness and stability. Application of these ceramics requires better understanding of their mechanical behavior in small scales and at elevated temperatures. Here, we prepared a ZrB2-ZrC ceramic eutectic composite, consisting of self-assembled ZrC rods grown within a single-crystalline ZrB2 matrix, and studied the mechanical properties of the individual eutectic phases using nanoindentation at both room and elevated-temperatures. The Vickers hardness of the eutectic composite was measured at room temperature. These data provide insight into the understanding of the mechanical behavior of the individual phases of non-oxide ceramic eutectic composites for high-temperature applications.

MICROSCOPIC FEATURES OF CEMENT PASTE MODIFIED BY FINE PERLITE

The use of waste material and replacement of binder element in cementitious composites is in focus of material development. Perlite in the construction industry is usually used in form of lightweight aggregate enhancing the insulating performance of concrete. This paper focuses on integration of fine perlite into the cement matrix and possible replacement of the cement binder in the composition of the material. The macromechanical performance of the modified paste is tested on specimens with 5, 10, 15 and 20% fine perlite substitution and pure cement sample. To distinguish the effect of the perlite on the microstructural level, pure cement material and specimen containing 10% of fine perlite are investigated by the electron microscopy. Furthermore, the mechanical properties of individual phases are examined and compared on same samples by instrumented indentation. The presented results enabled estimation of fine perlite impact on the macro and microscopic performance of the material.

Local heterogeneity in the mechanical properties of bicontinuous composites made by liquid metal dealloying

Bicontinuous composites made by liquid metal dealloying are excellent structural materials, with a unique combination of size-dependent strengthening and facile fabrication. However, due to the stochastic nature of dealloying, the local composition of individual ligaments can vary significantly and it is an open research question how this affects the bulk mechanical behavior. In this study, we use statistically significant nanoindentation to characterize the mechanical properties of individual phases in dealloyed bicontinuous composites. Through the analysis of several thousand indents, we correlate variances in the hardness and elastic modulus directly with the local microstructure and composition of the material.

TiTaCN-Co Cermets Prepared by Mechanochemical Technique: Microstructure and Mechanical Properties

Microstructure and mechanical characterization of (Ti,Ta)(C,N)-Co based solid solution cermets prepared by two mechanochemical synthesis processes (one- and two-step milling) and a pressureless sintering in protective helium atmosphere. Materials with composition of TixTa1-xC0.5N0.5-20%Co with two different Ti/Ta ratios (x = 0.9 and x = 0.95) were developed to prepare four groups of experimental materials. Microstructures were observed using confocal microscopy and grain size was evaluated using image analysis. Mechanical testing was carried out using nanoindentation equipment and nanohardness and indentation Young's modulus were obtained. Mechanical properties of individual phases were measured using single load/unload method with 20 mN maximum load (40 mN/min loading rate and maximum 10 s holding time for each indent). Mechanical properties of each material as a bulk were obtained also by single load/unload method with 300 mN maximum load (600 mN/min loading rate and maximum 10 s holding time). The resulting mechanical properties were comparable to that of typical industrial hardmetal cermets. Two-step milling resulted in finer microstructure but a wider range of grain size distribution. No significant dependence between mechanical properties and number of milling steps was found. However, the materials with higher amount of Ta showed slightly higher indentation elasticity modulus.

Global and local deformation behavior and mechanical properties of individual phases in a quenched and partitioned steel

Third generation advanced high strength steels produced via quenching and partitioning (Q&P) treatment are receiving increased attention. A 0.25C–3Mn–1.5Si–0.023 Al steel was subjected to Q&P processing (with varying partitioning temperature and time) resulting in the formation of complex multi-phase microstructures. The effect of Q&P parameters on the microstructure and morphology of microconstituents was analyzed. Mechanical properties of the material and of its individual microconstituents were studied via tensile testing and nanoindentation on individual microconstituents, which were identified a priori by electron back-scattered diffraction analysis. Special attention is paid to the effect of the morphology of retained austenite on its transformation stability. In situ tensile tests and digital image correlation analysis were performed to study deformation behavior of the Q&P processed steel at the micro-scale with respect to the local microstructure. The effect of local microstructure and properties of individual phases on the degree of strain partitioning is discussed.

Analysis of Mechanical Properties of Individual Phases in Steels by Depth Sensing Indentation

The macroscopic mechanical properties of steel are highly dependent upon microstructure, morphology, and distribution of each phase present. Nanomechanical testing (Depth sensing indentation) provides a straightforward solution for quantitatively characterizing each of these phases because it is very powerful technique for characterization of materials in small volumes. Measuring the intrinsic properties of each phase separately in multiphase materials gives information that is valuable for the development of new materials and for modelling [1]. In this work, depth sensing indentation has been used to reveal mechanical properties of different phases in steel sheets.

Investigation on microstructures of cementitious composites incorporating slag

Cementitious composites incorporating slag were investigated by multiple techniques, including scanning electron microscopy with backscattered electron and energy-dispersive X-ray spectroscopy detectors, thermogravimetric analysis, instrumented nanoindentation and ultrasonic measurements. The physical and mechanical properties of individual phases in cementitious composites with and without slag at different water to binder ratios were studied and are reported here. Subsequently, based on the identified phase properties, the macroscopic elastic moduli were calculated through a micromechanical method and verified with the experimental data. The results of this study show that the physical and mechanical properties of hydration products in cementitious composites incorporating slag are quite different from those of pure cement pastes. To explain the differences and improve scientific understanding of the influence of slag on the properties of hydration products, the composition, microstructures and mechanical properties were linked together for cementitious composites incorporating slag through this study.

Mechanical properties of individual phases, deformation and fracture in mechanically alloyed Al-Al<SUB align=right>4C<SUB align=right>3 composite

Using a Depth Sensing Indentation technique (DSI), the Martens hardness HM, indentation modulus EIT and deformation work W for Al matrix and Al4C3 particles have been measured. It has been shown that the hardness of Al4C3 particles is 57 times higher than the hardness of matrix. The change in fracture for the Al-12Al4C3 system was investigated and analysed at different temperatures and strain rates. With increasing tensile load, local cracks are formed by rupture of large particles and by decohesion of smaller particles from the matrix. Further increase of load leads to the crack growth by coalescence of cavities.

Nanoindentation study of Zn-based Pb free solders used in fine pitch interconnect applications

Because of their hazardous nature, conventional Sn–Pb solders are slowly being replaced by Pb free solders. Sn–Zn solder alloys have been identified as a potential alternative because of their low melting point close to that of Sn–Pb solder. However, the high Sn content and reflow temperature will accelerate intermetallic compound (IMC) formation at the solder/substrate interface, which in turn controls the reliability of the solders joints. A detailed study of the growth morphology of IMCs in solder joints will enhance our ability to control their influence on the mechanical and physical properties. Knowledge of the mechanical properties of individual phases makes predictions of the mechanical behavior of an overall joint more straightforward. The small length scale of intermetallic phase formation may lead to a behavior different from bulk samples. One would like to measure the mechanical properties of the phases in interesting realistic geometries. However, even low-load microhardness testing results in indentations that span multiple phases within a real joint. In the present work, the micromechanical properties of Pb-free solder joints such as Sn–8 wt.% Zn–3 wt.% Bi/Au/Ni/Cu were probed using nanoindentation. Nanoindentation is a reliable technique in testing small volumes of materials and complex microstructures manifested in the fine pitch interconnects employed in the flip-chip technologies. The IMCs formed between Zn and Au, and Ni, Zn were characterized and their hardness, elastic modulus were investigated in the present work. The IMCs are found to be ɛ-AuZn 8; δ-NiZn 8 compounds and formation of these compounds are found to depend on reflow temperature and time. It is also found that the hardness and modulus of the δ-NiZn 8 is higher than that of the ɛ-AuZn 8 compound.

Stochastic calibration of local constitutive models through measurements at the macroscale in heterogeneous media

A methodology is presented suitable to identify properties of single phases, locally at the microscale, within a heterogeneous periodic material, on the basis of measurements at the macroscale and homogenization techniques. Reference is made to periodically perforated steel sheets, regarded as a prototype of a ductile composite material with periodic microstructure. The proposed method might be applied to industrial situations where the fabrication process of a composite material alters the mechanical properties of individual phases or constituents. Experimental data are obtained through monotonic uniaxial tensile tests at the macroscale. An elastic–plastic hardening model is attributed to the matrix material. Weighted least-squares, Monte Carlo simulations and sequential non-linear Kalman filters are employed to solve the parameter identification problem in a stochastic context, and comparative assessments of diverse strategies of inverse analysis are presented, as to accuracy and computational effectiveness.