Hard Brittle Phase Research Articles

Effect of Strain Hardening on Wear Resistance Property of 316 Austenitic Stainless Steel

The main purpose of this investigation was to study the effect of strain hardening on wear properties of 316 austenitic stainless steel (ASS). Cold deformation was performed by using a universal tensile machine for 20% CW and 40% CW followed by heat treatment to relieve internal stresses. A secondary cold working process was performed for the heat-treated samples followed by a secondary heat treatment. Wear test measurements and microscopic examinations were preformed for all samples. It was observed that by increasing the strain hardening percentage the hard brittle martensite phase increases. Also, by increasing both the SiC grit of the emery papers (which was used in the wear test) and the time of the wear test, the weight lost per unit area was decreased. The wear resistance was increased by using single and double 20% strain hardening but by exceeding the cold working to more than 40% the wear resistance decreased.

Solid-state deposition of Mo-doped CoCrFeNi high-entropy alloy with excellent wear resistance via cold spray

To improve the wear resistance of CoCrFeNi high-entropy alloys (HEAs) for a wider range of industrial applications, the alloying strategy was applied to CoCrFeNi HEA by doping Mo element in various ratios, and CoCrFeNiMox (x = 0, 0.2, 0.5, and 1.0) HEA deposits were fabricated by cold spray. The microstructure evolution, mechanical properties, and tribological properties of cold-sprayed CoCrFeNiMox HEA deposits were systematically investigated. The results showed that Mo0, Mo0.2, and Mo0.5 deposits have a face-centered-cubic (FCC) single structure, while Mo1.0 deposit was composed of FCC matrix and hard brittle phases. The doping of Mo element into CoCrFeNi HEA deposits significantly increased the hardness due to the enhanced solid solution strengthening and precipitation strengthening. As a result, the anti-wear properties of Mo-doped CoCrFeNi HEA deposits were gradually improved with the increase in Mo ratios. To be specific, the Mo1.0 deposit exhibited the lowest specific wear rate of 5.1 × 10−5 mm3/N·m, which was reduced by 94.9% in comparison to the Mo0 deposit. Overall, the current study proposes a new strategy to manipulate the mechanical properties of cold-sprayed HEA deposits by alloying.

Vacuum diffusion bonding between Ni3Al-based superalloy and S31042 steel by surface self-nanocrystallization treatment

Vacuum diffusion bonding at a relatively low temperature is a recognized method for restraining intermetallics and optimizing joint microstructure. The surface self-nanocrystallization (SSN) treatment by shot peening technology is applied on the surface before bonding a couple of Ni3Al-based superalloy and S31042 steel, which lowers the bonding temperature for achieving a sound joint by 100 °C. Moreover, the joint strength of samples bonding at 1000 °C after SSN treatment is 178 MPa higher than that of the bonded samples at 1100 °C without SSN treatment. SEM, XRD and TEM analyses indicate SSN treatment improves bonding efficiency by increasing surface micro-deformation and introducing nanocrystalline and deformed layer. The formation of disordered Ni-solution on the surface makes γ’ strengthening phase re-precipitates in the joint and hard-brittle phase of AlN is restrained by diffusion bonding at 1000 °C. The good metallurgical bonding, re-precipitated γ’ phase and the formation of refining grains zone near the bonding interface contribute to the good performance of 1000 °C-bonded samples after SSN treatment.

Effect of holding time and Ti/B molar ratio on microstructure and mechanical properties of in-situ TiB2/Al composites fabricated by mixed salt reaction

In this study, in situ TiB2/Al composites is fabricated by K2TiF6 and KBF4 systems. The effects of process parameters on the size, distribution and morphology of in situ TiB2 particles, as well as the microstructure and mechanical properties of the composite is analyzed. When the mixed salts is added at 750 °C, TiB2 particles are short rods. When the temperature is higher than 825 °C, TiB2 particles are cubic columns and hexagonal columns. When the reaction temperature is 825 °C, the grain refinement of the composite is most obviously. When the holding time is 80 min, TiB2 particles are uniformly distributed in the matrix and the size is less than 2 μm. The ultimate tensile strength, yield strength and elongation of the composite reach the maximum values of 230 MPa, 125 MPa and 9.5%. When the holding time is 110 min, TiB2 particles agglomerate at the grain boundary, and the mechanical properties of the composites decrease. When the Ti/B molar ratio is 1/1, in addition to forming TiB2 particles, large size hard brittle phase TiAl3 appear in the microstructure. When the Ti/B molar ratio is 1/2.2, the formation of hard brittle phase TiAl3 can be inhibited, TiB2 particles are uniformly distributed in the matrix and the grain refinement is most obviously. The ultimate tensile strength, yield strength and elongation of the composite reach the maximum values of 225 MPa, 110 MPa and 8.5%. When the Ti/B molar ratio is 1/3, the unreacted residual mixed salts appear in the microstructure of the composite, and the residual mixed salts impurities exist at the interface between TiB2 particles and the matrix, so reduce the mechanical properties of the composite.

Significantly elevated strength of W-Ni3Al alloy by adding trace boron element

W-Ni3Al alloys have potential application in kinetic energy penetrator, but there are some problems such as high sintering temperature, large tungsten grain size, and poor mechanical properties. In this study, fine-grained W-Ni3Al-B alloys with excellent mechanical properties were successfully fabricated at a low temperature of 1150 °C by adding trace boron powder (B) and using spark plasma sintering (SPS). For the addition of B in the W-Ni3Al alloys, the low melting point B2O3 phase was formed and its thermite reaction released extra heat, promoting the sintering of the alloys. However, with the increasing of B content (0.1–0.7 wt%), the more hard brittle phases were formed, damaging the strength of sintered alloys; at the same time, the more B2O3 phase was evaporated due to the more released heat, causing occurrence of pores. Among all B-containing W-Ni3Al alloys, the 0.1B alloy exhibited the optimal mechanical properties with the bending strength of 1375.88 ± 19.20 MPa (higher 99.32% than that of the 0B alloy) and a high hardness value of 71.6 ± 0.29 HRA. By analyzing 0.1B alloy's microstructure, its good mechanical properties were related to the small tungsten grain size, heterostructural binder phase, minimal formation of hard brittle phases, dislocation movements being obstructed by the Al2O3 phase, and the tungsten transgranular cleavage fracture mode.

Wear and Corrosion Resistance of FeCoCrxNiAl High-Entropy Alloy Coatings Fabricated by Laser Cladding on Q345 Welded Joint

High-entropy alloy (HEA) coatings on the surface of low-alloy steel by laser cladding can improve the corrosion and wear resistance, and the performance can be further improved by adding the Cr element. However, the effect of Cr content on the microstructure, hardness, wear and corrosion resistance of the coatings on the welded joint has not been completely understood in the literature. This paper aims at revealing the influence of Cr content on the microstructure and properties of laser-cladded FeCoCrxNiAl HEA on different regions of Q345 welded structure. The results indicate that FeCoCrxNiAl HEA coating has good metallurgical bonding with the Q345 welded surface. The increase of Cr element content in the powder plays an important role in energy absorption of powder and substrate, affecting the dilution rate and diffusion of Fe from the substrate to HEA coating. The HEA coating is mainly composed of the face-centered cubic phase (FCC) and body-centered cubic phase (BCC). When x = 1.5, the actual Cr element content of coating is the highest, which promotes the formation of hard brittle phase BCC, and subsequently affects the hardness and wear resistance of the sample. Meanwhile, the corrosion resistance increases and then decreases, and reaches the highest when x = 1.5. Due to the existence of Cr and other elements with good corrosion resistance in the HEA coating, a dense oxide film can be formed in 3.5 wt.% NaCl solution and neutral salt spray environment to prevent the corrosion from continuing, which can effectively improve the corrosion resistance of each region of the welded joint, and the protective efficiencies on the weld bead (WB), heat-affected zone (HAZ) and base metal (BM) are 99.1, 98.4 and 96.6%, respectively.

Bioinspired multilayered cellular composites with enhanced energy absorption and shape recovery

Inspired by the multiscale configuration of the microstructure of cork, the paper describes the design, 3D printing, and evaluation of a new type of multilayered cellular composite (MCC) structure composed of hard brittle and soft flexible phases. The mechanical behavior of 3D printed MCC structures have been investigated both experimentally and numerically. The experiments show that the MCC structure absorbs four times the amount of energy of a conventional cellular configuration under compressive strains up to 70 %. Finite element simulations and 2D digital image correlation (DIC) also show that the multilayered architecture provides a more uniform strain distribution and higher stress transfer efficiency, with a resulting progressive failure mode rather than a catastrophic one. Cyclic loading tests demonstrate that the MCC structure also possesses exceptional shape recoverability under compressive deformations up to 40 %. These remarkable performance characteristics result from synergies between the properties of the two constituent materials and the chosen multilayered cellular microstructure. The soft phase, in particular, plays a pivotal role in absorbing elastic energy during loading and then releasing the stored energy while unloading. The volume fraction of the soft phase is also essential to control energy absorption and the transition of failure modes. The deformation mechanisms demonstrated here are robust and applicable to other architected cellular materials across multiple length scales and suggest new ways to design lightweight and high-resilience structural materials.

Nd:YAG pulsed laser brazing of cBN to steel matrix with Zr modified Ag–Cu–Ti active brazing alloy

The study was to investigate the modifying effect of the active element Zr on the properties of mechanical alloyed (MA) AgCu28–4.5Ti brazing alloys, especially the joint performance of cubic boron nitride (cBN)/45 steel brazed with AgCu28–4.5Ti–4Zr active brazing alloy. The brazing process was carried out using an Nd:YAG pulsed laser device under a high purity argon atmosphere. The granularity distribution and composition analysis of the MA brazing alloys, microstructural examinations and phase analysis were performed using a laser granularity analyzer, scanning electron microscopy (SEM) equipped with energy dispersion spectrometry (EDS), and X–ray diffraction (XRD) techniques. The results indicate that the alloy particles are refined, sizes are uniform, and the formation of the hard-brittle phase is reduced owing to the addition of the active element Zr. The wettability of the brazing alloy containing Zr is enhanced. The reaction of the active element Zr with Ag or Cu inhibits the combination of Ti with Ag or Cu under rapid laser heating and cooling, and further promotes the generation of TiB and TiN compounds. The joining mechanism is derived from the formation of a continuous reaction layer between cBN and the brazed alloy, containing a sub-outer structure of TiB, TiB2, TiN, ZrB2, and an outer structure consisting of AgZr2, Cu10Zr7. This multi-layered structure, which is from cBN to 45 steel, realizes the metallurgy combination of the brazing alloy and cBN particles. The friction and wear tests indicate that the reliable connection of cBN to steel is realized.

Microstructures and mechanical properties of A356/2024 bimetals fabricated by solid-liquid roll bonding

The present study investigates the process of solid-liquid roll bonding to fabricate A356/2024 Al alloy bimetals. The microstructure, elemental distribution, crystalline structure, hardness, and shear strength near the A356/2024 interface are systematically evaluated. The results demonstrate that cracks, pores, and other defects at the A356/2024 interface gradually disappear as the liquid pouring temperatures and the solid preheating temperatures are increased. At low liquid pouring temperatures or solid preheating temperatures, alloying elements at the interface form hard brittle phases such as Al2CuMg and CuAl2 intermetallics, resulting in high hardness values and reduced bonding strength at the interface. At high pouring temperatures or preheating temperatures, the alloying elements diffuse across the interface, and form a transition zone. The hardness increases gradually in the transition zone, which reduces the interfacial stress, and enhances the bonding strength of the interface. The interfacial shear strength progressively increases with increasing pouring temperatures, and attains a maximum value of 48.4 MPa at a relatively high pouring temperature of 720 °C in the absence of preheating. With preheating at 500 °C, the interfacial shear strength attains a maximum value of 57.93 MPa under the optimum process parameters including a relatively low pouring temperature of 680 °C.

A novel core-shell structure reinforced Zr-based metallic glass composite with combined high strength and good tensile ductility

Using the ZrO2 particles as precursor, a novel α-Zr/β-Zr core-shell structure reinforced Zr-based metallic glass (Zr-BMG) composite was fabricated. The oxygen is mainly concentrated in the α-Zr core, resulting in the very high hardness of α-Zr core. The β-Zr shell contained the relatively moderate amount of oxygen still has good ductility and work hardenability. The α-Zr/β-Zr core-shell structure reinforced Zr-BMG composite combined the advantages of the soft ductile and hard brittle phase reinforced BMG composites, and thereby exhibits the high strength and good tensile ductility. These findings give a new perspective to adjust the mechanical properties of the BMG composites.

Multilayered Al/Ni energetic structural materials with high energy density and mechanical properties prepared by a facile approach of electrodeposition and hot pressing

With an aim to fabricate multilayered Al/Ni energetic structural materials integrating high energy density and mechanical properties, a facile approach of electrodeposition and hot pressing was employed in this study. The effect of hot pressing time on exothermic reactions and mechanical properties has been systematically investigated. It was found that the exothermic heat of Al/Ni energetic structural materials decreased from 1003J/g to 782J/g, while the hot pressing process increased from 0.5 h to 4 h, and the initial exothermic reaction temperature declined simultaneously. Because of the increasing crystallite sizes of Ni and Al layers at hot pressing time of 1 h, Al/Ni multilayered materials acquired the maximum elongation, the minimum tensile strength and the lowest compressive strength. As the hot pressing process exceeded 2 h, the elongation deteriorated sharply and the compressive strength aggrandized significantly owing to the formation of the hard brittle Al3Ni phases in Al/Ni interfaces.

Structural Properties and Phase Stability of Primary Y Phase (Ti₂SC) in Ti-Stabilized Stainless Steel from Experiments and First Principles.

The morphology and microstructural evaluation of Y phases in AISI 321 (a Ti-stabilized stainless steel) were characterized after hot deformation. The electronic structure and phase stability of titanium carbosulfide were further discussed by first-principle calculations. It was found that Y phases, like curved strips or bones in AISI 321 stainless steel, mostly show a clustered distribution and are approximately arranged in parallel. The width of the Y phase is much less than the length, and the composition of the Y phase is close to that of Ti2SC. Y phases have exceptional thermal stability. The morphology of Y phases changed considerably after forging. During the first calculations, the Ti2SC with hexagonal structure does not spontaneously change into TiS and TiC; however Ti4S2C2 (Z = 2) can spontaneously change into the two phases. The Ti–S bonds are compressed in Ti4S2C2 cells, which leads to poor structural stability for Ti4S2C2. There is a covalent interaction between C/S and Ti, as well as an exchange of electrons between Ti and S/C atoms. Evidently, the mechanical stability of Ti4S2C2 is weak; however, Ti2SC shows high stability. Ti2SC, as a hard brittle phase, does not easily undergo plastic deformation.

Comparative study on the joining performance of TiH2 and ZrH2 modified AgCu28 brazing alloys with pulsed laser welding-brazing

Brazed alloys between cubic boron nitride (cBN) grits and matrix extremely affect the service life of the grinding wheel. The aim of this study was to investigate the addition of elemental Zr to improve the connection effect of alloys. The plates of pure titanium (Ti) Gr. 1 and AISI 1045 steel had been applied to conduct the welding-brazing experiments with active brazing alloys of AgCu28-4.5Ti and AgCu28-4.5Ti-4Zr. Brazing alloys was heated with an Nd:YAG pulsed laser welding-brazing system under inert argon gas atmosphere. Transition zones between the brazed alloys and matrices were investigated with scanning electron microscope (SEM), energy dispersion spectrometer (EDS), and X-ray diffraction (XRD) analyses. In addition, hardness of the brazed layer was analyzed as well as tribology. The results showed that the active element, zirconium (Zr), significantly accelerated the bidirectional diffusion and improved the gradient evolution of the main elements in the transition zones. Compared to Zr-free brazing alloys, the active element, Zr, inhibited the overproduction of the hard-brittle phase of Cu3Ti and formed other intermetallic compounds, such as AgZr2 and Cu10Zr7, which were beneficial to the metallurgical joint. A brazed layer with a lower friction coefficient, a more uniform hardness distribution, and better ductility was obtained, though the wear resistance slightly decreased. A solid solution product of Zr-Cu was formed during laser welding-brazing process, which strengthens the brazed layer and improves its overall performance.

Brittle-Ductile Transition in Laser 3D Printing of Fe-Based Bulk Metallic Glass Composites

The effects of the α-Fe phase on mechanical properties and cracking of laser 3D printing Fe-based bulk metallic glass composites were investigated. The elastic recovery and plasticity index were characterized by nanoindentation. As the volume fraction of the α-Fe phase increases from 23.66% to 52.38%, the elastic modulus of printed samples suddenly drops. The samples exhibit a lower deformation resistance, and the plasticity index increases gradually. When the volume fraction of the α-Fe phase is 67.84%, the interaction between the α-Fe phase and matrix phase is smaller during expansion shrinkage. As a result, cracking is easy to initiate, which leads to the highest crack rate of the printed sample. However, as the volume fraction of the α-Fe phase increases to 83.31%, the hard brittle phase was sandwiched between the α-Fe phases similar to the finger structure plays key role in the plastic deformation. The plastic deformation releases large amounts of stress concentrated at the boundary and suppresses crack formation.

Study on failure mode and mechanism of tool in friction stir welded steel

The failure modes and mechanism of the tool in friction stir welding process are stud ied by welding of Q235 steel of 4mm thick, with the tool made of YG8 Cemented carbide. The results show that the main failure modes of the tool in FSW of Q235 steel are the mechanical wear, the oxidation, the brittle fracture of the pin, and the concave and convex ring area on the shoulder. The microstructure, fracture morphology and micro-hardness of the tool are analyzed, it can be shown that the main reason for the failure are the high temperature friction of the tool for a long time, resulting in uneven or partial diffusion of the Co phase, and the tungsten carbide particles are peeled off from the matrix under the action of force, which seriously destroys the matrix model of the cemented carbide. The free carbon and the hard-brittle phase Co6W6C in the crystal boundary greatly weakens the solid solution strengthening of the Co phase to tungsten carbide, which decreases the hardness, strength and wear resistance of the tool.

Investigation on Ti6Al4V-V-Cr-Fe-SS316 Multi-layers Metallic Structure Fabricated by Laser 3D Printing

Joining titanium alloy and stainless steel is becoming an urgent need since their outstanding mechanical properties can be utilized integratedly. However, direct fusion joining of Ti6Al4V to SS316 can cause brittle Ti-Fe intermetallics which compromise join bonds’ mechanical properties. In this research, Laser 3D Printing was applied to explore a new Ti6Al4V to SS316 multi-metallic structure. A novel filler transition route was introduced (Ti6Al4V → V → Cr → Fe → SS316) to avoid the Ti-Fe intermetallics. Two experimental cases were performed for comparison to evaluate this novel route’s effect. In the first case, SS316 layer was directly deposited on Ti6Al4V substrate by laser 3D printing, but the sample cracked in the printing process. Then fracture morphology, phase identification, and micro-hardness were analyzed. In the second case, a multi-metallic structure was fabricated via laser 3D printing following the transition route. Microstructure characterization and composition distribution were analyzed via scanning electron microscope(SEM) and energy dispersive spectrometry(EDS). x-ray diffraction(XRD) tests demonstrated the intermetallics were effectively avoided following the transition route. Vickers hardness number(VHN) showed no significant hard brittle phases in the sample. Comparing with directly depositing SS316 on Ti6Al4V, the usage of the novel transition route can eliminate the intermetallics effectively. These research results are good contributions in joining titanium alloy and stainless steel.

In-situ bending under tension shear fracture analysis and microstructure “earthquake” of DP780 dual phase steels

Dual phase (DP) steels consist of hard brittle martensite phase and soft ductile ferrite phase. With a novel bending under tension test system, in-situ symmetrical bending under tension experiments were carried out and photomicrographs of bending surface were recorded. The microstructure “earthquake” of DP780 dual phase steels was observed in the bending under tension process. By analyzing the in-situ images serious, the initiation, coalescence of cavities and propagation of micro-cracks until final fracture were analyzed. The micro-cracks form only in the outside surface of bending radius, and mainly appear near the phase boundary of ferrite and martensite. Micro-cracks coalesce and propagate in the direction perpendicular to the stretching direction approximately, and at the phase boundary of martensite and ferrite. Furthermore, digital image correlation technology was used in this study to analysis the strain distribution between ferrite and martensite during the bending under tension deformation and fracture.

Fabrication and characterization of a functionally graded material from Ti-6Al-4V to SS316 by laser metal deposition

In this study, laser metal deposition (LMD) was employed to explore a new fabrication process for producing a functionally graded material (FGM) from Ti-6Al-4V to SS316. A transition composition route was introduced (Ti-6Al-4V→V→Cr→Fe→SS316) to avoid the intermetallic phases between Ti-6Al-4V and SS316. A thin wall sample was fabricated via LMD by following the transition composition route. Microstructure characterization and composition distribution analyses were performed by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The SEM images depicted the microstructural morphology of the FGM sample. The element gradient distribution determined by the EDS results may reflect the FGM transition composition route design. X-ray diffraction tests were conducted and the results demonstrated that the generation of intermetallic phases effectively avoided following the composition route. The Vickers hardness test was used to determine the Vickers hardness number (VHN) distribution from Ti-6Al-4V to SS316. The VHN results showed that no significant formation of hard brittle phases occurred in the LMD procedure.

Fracture initiation in multi-phase materials: A systematic three-dimensional approach using a FFT-based solver

This paper studies a two-phase material with a microstructure composed of a hard brittle reinforcement phase embedded in a soft ductile matrix. It addresses the full three-dimensional nature of the microstructure and macroscopic deformation. A large ensemble of periodic microstructures is used, whereby the individual grains of the two phases are modeled using equi-sized cubes. A particular solution strategy relying on the Fast Fourier Transform is adopted, which has a high computational efficiency both in terms of speed and memory footprint, thus enabling a statistically meaningful analysis. This solution method naturally accompanies the regular microstructural model, as the Fast Fourier Transform relies on a regular grid.Using the many considered microstructures as an ensemble, the average arrangement of phases around fracture initiation sites is objectively identified by the correlation between microstructure and fracture initiation – in three dimensions. The results show that fracture initiates where regions of the hard phase are interrupted by bands of the soft phase that are aligned with the direction of maximum shear. In such regions, the hard phase is arranged such that the area of the phase boundary perpendicular to the principal strain direction is maximum, leading to high hydrostatic tensile stresses, while not interrupting the shear bands that form in the soft phase. The local incompatibility that is present around the shear bands is responsible for a high plastic strain. By comparing the response to a two-dimensional microstructure it is observed that the response is qualitatively similar (both macroscopically and microscopically). One important difference is that the local strain partitioning between the two phases is over-predicted by the two-dimensional microstructure, leading to an overestimation of damage.

Effect of Hf content on martensitic transformation, microstructure, and mechanical properties of Cu50Zr50−xHfx alloys

The effect of Hf substituting for Zr of Cu50Zr50−xHfx alloys on the microstructure, martensitic transformation behavior, and mechanical properties is investigated. It is demonstrated that Cu50Zr50−xHfx alloys exhibit higher transformation temperature with a peak martensite reverse transformation temperature of 594 K for Cu50Zr42Hf8 alloy, smaller thermal hysteresis and better thermal stability in comparison to those of Cu50Zr50 alloy. Due to the appearance of hard brittle second phase (Zr,Hf)2Cu, the elastic modulus increases while the plasticity reduces with Hf substituting for Zr.