Homogeneous Microstructure Research Articles

Influence of Electron Beam Powder Bed Fusion Process Parameters at Constant Volumetric Energy Density on Surface Topography and Microstructural Homogeneity of a Titanium Aluminide Alloy

In powder bed fusion additive manufacturing, the volumetric energy density E V is a commonly used parameter to quantify process energy input. However, recent results question the suitability of E V as a design parameter, as varying the contributing parameters may yield different part properties. Herein, beam current, scan velocity, and line offset in electron beam powder bed fusion (PBF‐EB) of the titanium aluminide alloy TNM–B1 are systematically varied while maintaining an overall constant E V. The samples are evaluated regarding surface morphology, relative density, microstructure, hardness, and aluminum loss due to evaporation. Moreover, the specimens are subjected to two different heat treatments to obtain fully lamellar (FL) and nearly lamellar (NLγ) microstructures, respectively. With a combination of low beam currents, low‐to‐intermediate scan velocities, and low line offsets, parts with even surfaces, relative densities above 99.9%, and homogeneous microstructures are achieved. On the other hand, especially high beam currents promote the formation of surface bulges and pronounced aluminum evaporation, resulting in inhomogeneous banded microstructures after heat treatment. The results demonstrate the importance of considering the individual parameters instead of E V in process optimization for PBF‐EB.

Preparation and characterisation of tin bronze/steel composites by solid–liquid bonding with vibration

In the present study, mechanical vibration was applied in the preparation of the tin bronze/steel bimetal composite by the solid–liquid bonding, and the effects on the microstructure and mechanical properties were investigated. The results show that mechanical vibration refines the microstructure of tin bronze and accelerates the interdiffusion between the two components, resulting in the improvement of the bonding strength and Brinell hardness. With the vibration frequency of 30 Hz, the composite strength and hardness are significantly improved. The finite element method further shows that the exciting force and homogeneous temperature field caused by the vibration are the main reasons for the microstructure optimisation. HIGHLIGHTS The tin bronze/1010 steel bimetallic layered composites with homogeneous microstructure are prepared by solid–liquid bonding under the mechanical vibration field. The interface thickness can be increased by applying mechanical vibration to the solid–liquid bonding process of the bimetals. Combined with the results of finite element simulation, the effect mechanism of the mechanical vibration in the preparation process was discussed. With the application of mechanical vibration, the hardness and interfacial bonding strength of the bimetals are obviously improved, and there is an optimal vibration parameter.

Study on Microstructure and Properties of Thermal Barrier Coating for Gas Turbine

Thermal barrier coating (TBC), which can protect the metallic components from hot gas, is one of the core technologies to achieve the development goal of higher thermal efficiency and lower emission for gas turbine. A double-coat TBC was prepared on the Mar M247 substrate of turbine blade for gas turbine which consisted of a CoNiCrAlY bond coat(BC) was prepared by high velocity oxygen fuel(HVOF) and a ZrO2-8Y2O3(8YSZ) top coat(TC) was prepared by atmospheric plasma spraying (APS).The microstructure of the TBC was analyzed by optical microscope(OM) and scanning electron microscope(SEM), and the thermal insulation and thermal shock resistance of the TBC were investigated. The results show that the homogeneous and fine microstructure in TBC is obtained,the interfacial bonding between the top coat and the bond coat, between the bond coat and the substrate is well. The thermal insulation temperature can reach 156°C,under the condition of test temperature of 1150°C and cooling air flow of 4 m3/h. And the thermal shock resistance is greater than 100 cycles at the test condition of 1050 °C.

Low Cost Biopolymer Adsorbents for the Removal of Heavy Metal Contaminant from Wastewater

AbstractPolymeric materials have been remarkably associated with our daily life. The hydrophilic/hydrophobic biopolymer systems have gained importance in the last few years, because of the environmental pollution of nonbiodegradable synthetic plastics. Recently, biopolymers with functional groups have been directly used for the fabrication of adsorptive membranes in order to avoid the undesirable morphology change of the membranes during the surface modifications. Compared with other modification technologies or a synthesis of totally new materials, biopolymer blending has several advantages like simplicity, reproducibility, and commercial feasibility. The valuable part of blending of biopolymers can be used for the preparation of new materials with improved physicochemical and mechanical properties. The objective of this work is the development of biomembranes based on a mixture of three biopolymers, that is, alginate (AL), chitosan (CS), and polylactic acid (PLA). Physical characterizations of the elaborated biopolymeric membranes are carried out by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and contact angle measurements. The SEM results show that the synthesized membranes exhibited homogeneous dense microstructures. The second objective of this paper is to evaluate the importance of these biopolymers in removing lead which is considered as toxic metal. In fact, all synthesized membranes are applied to the treatment of wastewater to eliminate heavy metals principally Pb2+.

Microstructural tailoring, mechanical and thermal properties of SiC composites fabricated by selective laser sintering and reactive melt infiltration

Poor flowability of printable powders and long preparation cycles are the main challenges in selective laser sintering (SLS) of chopped carbon fiber reinforced silicon carbide composites (SiC composites) with complex structures. In this study, we develop an efficient and novel processing route in the fabrication of lightweight SiC composites via SLS of phenolic resin (PR) and C_f powders with the addition of α-SiC particles combined with one-step reactive melt infiltration (RMI). The effects of α-SiC addition on the microstructural evolution of the C_f/SiC/PR printed bodies, C_f/SiC/C green bodies, and derived SiC composites were investigated. The results indicate that the added α-SiC particles play an important role in enhancing the flowability of raw powders, reducing porosity, increasing the reliability of the C_f/SiC/C green bodies, and contributing to improving the microstructure homogeneity and mechanical properties of the SiC composites. The maximum density, flexural strength, and fracture toughness of the SiC composites are 2.749±0.006 g×cm⁻³, 266±5 MPa, and 3.30±0.06 MPa·m^1/2, respectively. The coefficient of thermal expansion (CTE) of the SiC composites is approximately 4.29×10⁻⁶ K⁻¹ from room temperature (RT) to 900 °C, and the thermal conductivity is in the range of 80.15-92.48 W·m⁻¹·K⁻¹ at RT. The high-temperature strength of the SiC composites increase to 287±18 MPa up to 1200 °C. This study provides a novel as well as a feasible tactic for the preparation of high-quality printable powders as well as lightweight, high strength, and high thermal conductivity SiC composites with complex structures by SLS and RMI.

Integrating HIP and homogenisation heat treatment and its effect on the workability of a conventional peritectic TiAl alloy

The aim of this study was to understand how consolidation and homogenisation, as well as the possibility of integrating the two processes, influences the pre-compression microstructure and subsequent compression behaviour of an industry accepted, peritectic solidifying titanium aluminide ingot alloy; 45XD.This study differs from existing work with its emphasis on understanding the effect of integrating consolidation and homogenisation on workability, as well as how these processes influence the pre-and post-compression microstructure individually. This was assessed by the material's strain rate sensitivity in primary and secondary compression. The target microstructure was identified from the literature as being capable of a strain rate sensitivity of ≥0.3.The results presented here show that it is possible to integrate the consolidation and homogenisation stages, and this proved beneficial, namely achieving a high lamellar content and elementally homogeneous microstructure presented prior to compression. Subsequent deformation generated high values of dynamic recrystallisation fraction and globularisation returned upon primary compression, and the highest strain rate sensitivity at secondary compression, in comparison to material processed by the traditional approach. This is thought to be due to pressure and temperature during the integrated process reducing both segregation, seen through casting, and so the B2/β0 content compared to consolidated material. The integrated consolidation and homogenisation approach also prevented the grain growth seen in the traditional route; this is anticipated to be due to the two slow cooling stages involved in the traditional process rather than the effect of isostatic pressure.

Fatigue properties of as-built and heat-treated Inconel 625 obtained by the hybridization of two laser-powder based additive processes

Laser Powder Bed Fusion and Direct Energy Deposition processes have complementary characteristics. Their hybridization can increase the variety of applications for additive manufacturing. This paper investigates the static and fatigue behaviors of hybrid Inconel 625 parts using monotonic and high cycle fatigue tests, local strain measurements and self-heating method. Fatigue properties of as-built and recrystallized LPBF, DED and hybrid Inconel 625 were evaluated and compared. The effect of heat treatment on hybrid microstructure homogeneity was investigated. Their consequences on mechanical compatibility and fatigue strength were proved. The fatigue strength was attributed to the competition between defects and the strain compatibilities.

Cavitation Erosion Characteristics of the EN AW-6082 Aluminum Alloy by TIG Surface Remelting.

Components made of aluminum alloys operating under cavitation erosion conditions have low performance and therefore a reduced lifetime. The degradation of these components is a consequence of the repetitive implosion of cavitation bubbles adjacent to the solid surface. In this paper, the effect of the rapid re-melting and solidification modification of the surface microstructure of parts of an Al-based alloy strengthened by artificial ageing on the reduction of material loss through cavitation erosion was investigated. The heat source used was the electric arc generated between a tungsten electrode and the workpiece (i.e., TIG). Local surface melting was performed at different values of linear energy (El = 6600-15840 J/cm), varying the current between 100 A and 200 A, at a constant voltage of 10 V. The obtained results showed an increase in the surface microhardness at values of 129-137 HV0.05 and a decrease in the erosion rate from 0.50 µm/min, characteristic of the artificial ageing heat treatment, to 0.10-0.32 µm/min, specific to TIG re-melted layers. For the study of the cavitational erosion mechanism, investigations were carried out by optical microscopy and scanning electron microscopy. The results showed that the improvement of the cavitational erosion resistance by surface melting was a consequence of the increase in microstructural homogeneity and grains refinement.

Effect of heat treatment on microstructure evolution, phase transformation and corrosion resistance of Mg-4Zn-0.4Zr-1.0Sr alloy

The corrosion mechanism of Mg-4Zn-0.4Zr-1.0Sr alloy in the as-cast and heat-treated (T4, T6) states was investigated by scanning electron microscopy (SEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), immersion weight loss and electrochemical corrosion test. The results show that the long strips of the Mg17Sr2 phase precipitated along the grain boundaries in the as-cast state. The Mg17Sr2 phase is partially solid-solved into the matrix after heat treatment, and some Zr-containing particles precipitated in the T6 state are uniformly distributed on the surface of the alloy. It is shown that the T6 alloy has excellent corrosion resistance (0.39 ± 0.04 mm/y) due to the homogeneous microstructure and the uniform precipitated phase. In addition, corrosion products on the surface of the T6 alloy were detected to contain Sr-containing compounds as well as P-containing compounds, which are also important for improving the corrosion resistance of the alloy.

Preparation and optical properties of highly transparent MgAl1.9Ga0.1O4 ceramics via aqueous gel-casting method

The aqueous gel-casting technology has been widely used to prepare high-quality green body for various transparent ceramics with large dimension and complex shape. However, owing to the severe hydrolysis of MgAl2O4 powder, it is challenging to obtain thick aqueous slurry with high homogeneity and flowability. In this paper, the surface chemical state of MgAl2O4 powder was modified by introducing Ga3+, and stable MgAl1.9Ga0.1O4 aqueous slurry with high solid-phase loading (52 vol. %) and low viscosity (136 mPa·s, at a shear rate of 50 s-1) was successfully prepared. After pressureless presintering and hot isostatic pressing, the gel-cast sample exhibited much higher optical transmittance and more homogeneous microstructure than the dry-pressed sample, which is mainly derived from the improved homogeneity and densification of the green bodies and ceramics. The optical band gap, infrared cutoff wavelength, static refractive index and dispersion of both MgAl1.9Ga0.1O4 and MgAl2O4 transparent ceramics were systematically compared. It is indicated that the transparent MgAl1.9Ga0.1O4 ceramic has the increscent static refractive index of 1.695, the decrescent direct band gap energy of 6.15 eV and absorption coefficient of 0.49 cm-1 at 5 µm, which could be ascribable to the fact that Ga3+ has different electronic structure, higher electronic polarizability and larger ionic radius in comparison with Al3+. This work provides a dependable solution for preparation of spinel oxide ceramics with superior optical properties and large dimension.

Surface morphology, microstructure and mechanical properties of Al–Mg–Sc alloy thin wall produced by laser-arc hybrid additive manufacturing

The refined microstructure and enhanced mechanical properties of aluminum alloys containing Sc have attracted a great deal of attention in the recent past. In this work, a wire-based process of laser-arc hybrid additive manufacturing (LHAM) was developed and utilized to fabricate Al–Mg–Sc alloy thin wall deposits. The macro morphology, microstructural features and mechanical properties of LHAMed Al–Mg–Sc alloy were systematically investigated in comparison with wire and arc additive manufacturing (WAAM) under two processing conditions, i.e., same arc current (WAAM_SA) and same heat input (WAAM_SH). The surface quality of LHAMed deposits was significantly improved compared to that of WAAM_SA due to the stabilized effect of laser on arc behaviors. The deposits made by LHAM showed a refined and homogeneous microstructure compared to that of WAAM_SH under the condition of the same heat input, and a similar grain size with that of WAAM_SA even using a higher heat input. The microhardness results showed the LHAM had a higher and more stable microhardness distribution due to the homogeneous microstructure and less burning loss of magnesium. The as-deposited walls of LHAM and WAAM_SA showed a similar ultimate tensile strength (UTS) of more than 345 MPa for both horizontal and vertical directions, which is slightly higher than that of WAAM_SH. The as-deposited wall of LHAM also showed an exceptional elongation of about 26%, which is higher than that of both WAAM_SA and WAAM_SH samples, especially in the vertical direction, indicating less anisotropy in mechanical properties.

Dual-drug loaded polysaccharide-based self-healing hydrogels with multifunctionality for promoting diabetic wound healing

Diabetic chronic wound healing still faces huge clinical challenge. The arrangement and coordination of healing processes are disordered in diabetic wound caused by the persistent inflammatory response, microbial infection, impaired angiogenesis, resulting in the delayed and even non-healing wounds. Here, the dual-drug loaded nanocomposite polysaccharide-based self-healing hydrogels (OCM@P) with multifunctionality were developed to promote diabetic wound healing. Curcumin (Cur) loaded mesoporous polydopamine nanoparticles (MPDA@Cur NPs) and metformin (Met) were introduced into the polymer matrix formed by the dynamic imine bonds and electrostatic interactions between carboxymethyl chitosan and oxidized hyaluronic acid to fabricate OCM@P hydrogels. OCM@P hydrogels show homogeneous and interconnected porous microstructure, which possess good tissue adhesiveness, enhanced compression strength, great anti-fatigue behavior, excellent self-recovery capacity, low cytotoxicity, rapid hemostatic ability and robust broad-spectrum antibacterial activity. Interestingly, OCM@P hydrogels exhibit rapid release of Met and long-term sustained release of Cur, thereby to effectively scavenge extracellular and intracellular free radicals. Significantly, OCM@P hydrogels remarkably promote re-epithelization, granulation tissue formation, collagen deposition and arrangement, angiogenesis as well as wound contraction in diabetic wound healing. Overall, the multifunctional synergy of OCM@P hydrogels greatly contributes to accelerating diabetic wound healing, which demonstrate promising application as scaffolds in regenerative medicine.

Microstructure refinement of a cast high entropy alloy by thermomechanical treatments

This work investigates the hot compressive behaviour of a cast high entropy alloy. The alloy is subjected to four different thermomechanical treatments to refine the as-cast microstructure: hot compression tests at constant strain rates (0.001s−1 and 1s−1), hot compression tests with strain rate jumps (between 0.001s−1 and 1s−1), multi-stage hot deformation with holding intervals of 1 and 5 min, and hot compression at 0.1s−1 followed by annealing. The three first tests were carried out at 1100 °C and the deformation step of the last type was carried out at 1050 °C followed by annealing at 1150 °C. The deformation at 0.001s−1 promotes dynamic recrystallisation. Dynamic recrystallisation occurs when jumping from 1s−1 to 0.001s−1 and does not occur if the jump is from 0.001s−1 to 1s−1. Multi-stage interrupted tests show that 1 min holding between the stages promote dynamic recrystallisation, while static recrystallisation occurs more pronouncedly for 5 min inter-stage holding. Due to the large initial grain size, deformation does not occur homogeneously within the grains, and heterogeneous static recrystallisation occurs within the deformed specimen. Whether the alloy is solution heat treated or deformed in the as-cast condition does not affect the recrystallisation behaviour. Overall, refining the coarse cast microstructure of the investigated alloy is possible, although more deformation steps are needed to produce a homogeneous microstructure.

Microstructure and Mechanical Properties of Y4Zr3O12-Added Fe-13.5Cr-2W Oxide-Dispersion-Strengthened Steels, Containing High Contents of C and N, Prepared by Mechanical Alloying and Two-Step Spark Plasma Sintering.

Oxide-dispersion-strengthened (ODS) steel is considered as a promising candidate structural material for nuclear applications. In this study, the microstructure and mechanical properties of Y4Zr3O12-added Fe-13.5Cr-2W ODS steels, containing high contents of C and N, prepared by mechanical alloying (MA) and two-step spark plasma sintering (SPS), were investigated. The results showed that pure Y4Zr3O12 powders, with a grain size of 3.5 nm, were well prepared with NH3·H2O addition by the sol-gel method in advance, in order to avoid the formation of some coarse or undesired oxides. W was completely dissolved into the matrix after 48 h of ball milling at 300 rpm, and the main elements were uniformly distributed on the surface of the milled powders. The unexpected face-centered cubic (FCC, γ)/body-centered cubic (BCC, α) dual-phase structure of the sintered specimens, could be explained by the unexpectedly high contents of C and N from the raw powder production process, fast-sintering characteristic of SPS, and inhibitory effect of W on the diffusion of C. The experimental results were approximately consistent with the simulation results from the Thermo Calc software. The temperature combination of 800 °C and 1100 °C during the SPS process, provided a relatively more homogeneous microstructure, while the combination of 750 °C and 1150 °C, provided the highest ultimate tensile strength (UTS), of 1038 MPa, with the highest uniform elongation (UE), of 6.2%. M23C6, Cr2O3, M2(C,N), and other precipitates, were mainly distributed at grain boundaries, especially at the triple junctions, which led to Cr depletion at grain boundaries.

Influence of the Inherited Structure Induced by Al and Si Alloying on Microstructure Evolution and Mechanical Properties of 100Cr6 Steels

The fatigue lifetime of high‐strength 100Cr6 steels can be improved by an increased content of retained austenite that can be induced by Al and Si alloying. The related deformation‐induced retention of the austenite–martensite transformation during cyclic loading increases their local strain hardening capacity. However, for those 100Cr6 steels containing retained austenite, sufficient dimensional stability must be ensured. In this study, two standard 100Cr6 steels alloyed either with 1.5 wt% Al or 1.5 wt% Si (to diminish carbide formation and accordingly promote austenite retention) are laboratory melted and processed to adjust a microstructure of bainite, retained austenite, and carbides. The segregation simulation in the as‐cast condition and the corresponding microstructures in the forging and heat‐treating conditions are investigated. The inheritance of chemical heterogeneity leads to structural heterogeneity on both the nano‐ (nm) and micro (μm) scales. This heterogeneity is much more pronounced in the Al‐alloyed steel, which can be attributed to inheritance from the as‐cast state. While the results of the quasistatic tensile tests are comparable for both alloys, the cyclic load increase tests indicate a higher fatigue strength of the Si‐alloyed steel, which can be explained with the more homogenous microstructure and the finer distribution of the retained austenite.

Simulated diffusion spreadability for characterizing the structure and transport properties of two-phase materials

Time-dependent diffusion processes between phases of heterogeneous materials are ubiquitous in a variety of contexts in the physical, chemical, and biological sciences. Examples of such materials include composites, porous materials, geological media, cellular solids, polymer blends, colloids, gels, and biological media. The recently developed diffusion spreadability, S(t), provides a direct link between time-dependent interphase diffusive transport and the microstructure of two-phase materials across length scales (Torquato, 2021); thus making S(t) a powerful dynamic means for classifying all statistically homogeneous microstructures, spanning from anti-hyperuniform to hyperuniform. It was shown that the small-, intermediate-, and long-time behaviors of S(t) are directly determined by the small-, intermediate-, and large-scale structural features of the material. Moreover, the spreadability can be applied as a physical-property based tool for microstructural characterization in the absence of or as supplement to scattering information. In this work, we develop a computationally efficient algorithm for ascertaining S(t) directly from digitized representations of material microstructures via random-walk techniques. Our algorithm yields the time-dependent local walker concentration field c(x,t), a quantity not previously examined in the context of the spreadability, enabling us to compute the entropy production rate ṡ(t) of the associated diffusion process, which is a quantity related to the rate of energy dissipation. We also derive exact analytical expressions for ṡ(t), and find that hyperuniform materials have smaller dissipation than any nonhyperuniform materials. Lastly, we use our algorithm to compute, for the first time, the more general case of the spreadability in which the phase diffusion coefficients are distinct and provide a method for extracting the effective diffusion coefficient of the two-phase material from such data. We apply our algorithm to a variety of two- and three-dimensional simulated model (non)hyperuniform microstructures to assess their large-scale structures and diffusion properties. Given previously identified connections between the spreadability and certain nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) procedures, our algorithm is also pertinent to such experimental studies. Overall, our algorithm has practical use in the discovery and design of heterogeneous materials with desirable time-dependent diffusion properties.

Development of Bituminous Paint from Agbabu Natural Bitumen for Coat Coat-Protecting the Underparts of Automobile Chassis against Corrosion and Wear

To date, there has been continued demand for more effective, less expensive, and accessible coating systems for durable corrosion and wear protection of auto auto-bodies, with a research need to meet the demands. The rationale behind this study was to create a high high-quality, low low-cost bituminous paint for use in protecting the under parts of automobile chassis against corrosion and wear, particularly in Nigeria. Five paint blends containing various proportions of 70 –100% Agbabu natural bitumen, 02 02–5% kerosene, 0 0–8.5% cobalt, 0 0–1% pigment, and 0 0–2.1% lead drier were produced and characterized by their basic physicochemical properties. The blends were brush brush-coated to a 1.78 1.78-mm average thickness on plate samples of mild steel, a commonly and widely applied but highly corrosion corrosion-susceptible chassis material type. Corrosion and wear tests performed on the steel samples under 1.78 1.78-mm -thick hard hard-dried coatings of the paint blends revealed that the blend with 75% bitumen, 15% kerosene, 8% cobalt, 0.6% pigment, and 1.4% lead drier content could perform exceptionally well in protecting the steel a t the coating thickness. X X-ray fluorescence and scanning electron microscopy analyses of that paint blend were conducted to understand its distinct chemical compositions and microstructural homogeneity level. The 1.78 1.78-mm -thick coating of that paint blend’s adhesion adequacy to the steel was also investigated. Analyses of the collected data revealed that the blend contained 25 different chemical species that are benign to steel corrosion, had a more or less uniform microstructure demonstrating its homogeneity, had minimal intergranular boundaries indicating minimal ingress of corrosion corrosion-causing agents to the steel underneath its coatings, and its hard hard-dried thin coatings would have excellent adhesion to any ferrous chassis material..

Enhancing hardness and toughness of WC simultaneously by dispersed ZrO2

A novel method was proposed to achieve uniform dispersion of ZrO2 nanoparticles in the WC matrix. The prepared WC-ZrO2 ceramic exhibited outstanding mechanical properties with simultaneously high hardness and fracture toughness. It was disclosed that the high toughness of the present WC-ZrO2 ceramic results from the contributions of stress-induced phase transformation from t-ZrO2 to m-ZrO2, the homogeneous ultrafine microstructure with coherent WC/ZrO2 interface, and the stress release of WC in the vicinity of ZrO2. The later two factors enhance the fracture toughness by crack deflection and crack bridging. In particular, the contribution to toughness by phase transformation of ZrO2 is 1.9 and 2.7 times of that of the crack deflection and crack bridging, respectively. This study provides a strategy to increase toughness of ceramics greatly while keeping its high hardness.

Fabrication of (Ti-Al-Si)/(Ti-C)/Ti – layered alloy by SHS pressing

A metal-carbide-intermetallic material based on combustion products of the layer system (Ti-Al-Si)/(Ti-C)/Ti was for the first time obtained with the help of self-propagating high-temperature synthesis (SHS) combined with pressing. Exothermic synthesis from elementary powders was carried out at a pressure of 10 MPa, and pressing of the hot synthesis product was carried out at a pressure of 100 MPa. It has been shown that SHS pressing contributes to the formation of permanent joints of «metal/carbide/intermetallic» layers. The main features of microstructure formation, phase composition, and strength properties of transition zones at the boundary between reacting SHS compositions, Ti-C and Ti-Al-Si and Ti-metal substrate are investigated. It is shown that during SHS reaction, a homogeneous microstructure of Ti-C and Ti-Al-Si layers with an insignificant content of cracks and pores is formed. The thickness of the transition zone between the layers was at least 15 µm. The main phase formed in the combustion product of Ti-Al-Si layer is, according to the results of X-ray phase analysis, triple phase Ti20Al3Si9, the content of which, calculated by the Rietveld method, was at least 87 wt. %. In addition, the combustion product contains a secondary phase of Ti3Al in the amount of 13 wt. %. The energy dispersion analysis revealed that diffusion of aluminium through the titanium carbide layer into the titanium substrate to a depth of approx. 30 µm is observed. Microhardness value of the combustion product of Ti-Al-Si layer was about 10 GPa. The rectilinear nature of crack propagation in the synthesized combustion product of Ti-Al-Si layer, as well as the Palmquist crack resistance coefficient varying within 5.1-5.7 MPa·m1/2, indicate the fragility of the material.

3D microgel with extensively adjustable stiffness and homogeneous microstructure for metastasis analysis of solid tumor

3D microgels with various mechanical properties have been important platforms tumor metastasis analysis, and widely adjustable stiffness is crucial for deeper researches. Herein, by mixing biodegradable polylactic acid (PLA) nanofibers in the modified alginate with different concentrations of Ca2+, we significantly enhance the stiffness range of microgels while retaining the pore size, which provides bionic microenvironment for tumor analysis. As a proof of concept, we simulated the mechanical characteristics of breast tumors by encapsulating cells in 3D microgels with diverse stiffness, and analyzed cellular behaviors of two typical breast cancer cell lines: MCF-7 and SUM-159. Results showed that with the addition of 2.0% (w/v) PLA short nanofibers, the Young's modulus of modified alginate increased more than three-fold. Besides preserving high survival and proliferation rates, both cells also displayed stronger migration ability in soft microgel spheres, where RT-qPCR analysis revealed the underlying changes at the genetic level. This systematic study demonstrated our method is powerful for creating widely adjustable 3D mechanical microenvironment, and the results of cellular behavior analysis shows its promising application prospects in tumorigenesis and progression.