Precipitation Strengthening Mechanisms Research Articles

Effects of Nd content on the microstructures and mechanical properties of ZK60 Mg alloy and corresponding strengthening mechanisms

The aim of this research was to develop high-strength Mg alloys and investigate the microstructural evolution and corresponding strengthening mechanisms of ZK60 Mg alloys with different Nd content. The results indicated that the Nd-free ZK60 alloy was mainly composed of the α-Mg matrix and MgZn, MgZn2 and Zn2Zr phases, while a new phase, Nd3Zn11, formed after the addition of Nd. The addition of Nd enhanced the precipitation. The grain size first decreased and then increased with increasing Nd content. The texture component parallel to the ED in the [1‾ 100] direction remained unchanged after the addition of Nd, but the texture intensities sharply increased. The as-extruded Mg-6Zn-0.5Zr-3Nd (wt.%) alloy exhibited the best mechanical properties among all the as-extruded alloys, with the YS, UTS, and EL of 355 MPa, 369 MPa, and 8.9 %, respectively. The YS increased by 77 MPa compared with that of the as-extruded ZK60 Mg alloy, which was mainly attributed to the texture strengthening and precipitation strengthening mechanisms.

Impact of Vanadium Presence on the Mechanical and Microstructural Characteristics of a Dilute Al–Sc–Zr–Si Alloy During Isothermal Aging

In this work, we studied precipitation tendency and resulting ambient and elevated temperature properties in low-V (Al-0.06Sc-0.06Zr-0.18Si-0.05V at.%), high-V (Al-0.06Sc-0.06Zr-0.18Si-0.10V at.%), and free-V (Al-0.06Sc-0.06Zr-0.18Si at.%) alloys subjected to isothermal aging at 300 °C and 400 °C. Scanning transmission electron microscopy revealed that V incorporated into Al3(Sc, Zr) nano-precipitates during aging, forming Al3(Sc, Zr, V) while retaining the spherical morphology and L12 order. Analysis showed that V delays precipitation kinetics by interacting with vacancies, requiring longer aging for peak strength. Both V alloys demonstrated increased peak microhardness around 50–100 MPa relative to the free-V alloy after extended aging. V also reduced precipitate coarsening rates during overaging. However, creep testing exhibited no improvements to threshold stress, indicating V did not expand the precipitate/matrix lattice mismatch needed for enhanced creep resistance. The threshold stress changed from 10.2 MPa in the free-V alloy to 10.4 MPa and 10.1 MPa in the low-V and high-V alloys, respectively. Instead, V localization in the interface of nano-precipitates with matrix contributed more stability. The precipitation strengthening mechanisms in all alloys were studied using established models for L12-reinforced systems. The results showed that coherency and ordering strengthening are the primary active mechanisms.

Elucidating the tensile work hardening behaviour of precipitate containing Al0.3Co1.5CrFeNi1.5Ti0.2 high entropy alloy

A significant amount of work has been performed, since the last decade, on designing novel high entropy alloy (HEA) compositions. However, the effort on concluding a universal mechanism on the strain hardening behavior of these alloys with precipitates is limited. The current study is designed with an aim to comprehend the mechanical behavior of Al0.3Co1.5CrFeNi1.5Ti0.2 HEA in solution treated and aged conditions. The results show that the peak aged condition of sample contains two types of precipitates – B2 and L12 (γ′) of approximately 800 nm and 40 nm size, respectively. They are found to be responsible for a significant increase in strength in aged samples than solution treated ones. Deformation was found to occur mainly by planar slip on the {111} primary slip planes. Noticeable strain hardening behavior was attributed to the formation of stacking faults (SFs) and Lomer-Cottrell (LC) locks, inhibiting the dislocation motion. Numerous paired dislocations formed due to inhibition of slip by the ordered γ′ precipitates, coexist with a few Orowan loops in the peak-aged alloy after deformation. However, the primary strengthening mechanism was found to be the shearing of γ′ precipitates by partial dislocations. Shearing of nanosized γ′ precipitates by partial dislocations is energetically favourable for the system than shearing by full dislocations. Overall, this study enhances the understanding of the precipitation strengthening and strain hardening mechanisms in high entropy alloys.

Recrystallization behavior and strengthening mechanism of extruded Mg−Gd−Y−Zn−Zr alloy with different pre-aged states

Recrystallization behavior and strengthening mechanism of extruded Mg−Gd−Y−Zn−Zr alloy with different pre-aged states

Probing effects of solute trapping on the mechanical properties of α-Al in rapidly solidified hypoeutectic Al-10at.%Cu after surface laser melting

After scanned laser surface remelting the resultant rapid solidification microstructures of multicomponent alloys exhibit morphological gradients, with scale refinement and non-equilibrium features, including non-equilibrium solute trapping, which are associated with property changes. Combinations of site-specific mechanical property measurements by nano-indentation and microstructural analyses by electron microscopy have been used to determine microstructure-property relationships for the characteristic features of the rapid solidification microstructure of a hypo-eutectic Al–Cu alloy containing 10 atom percent Cu. A microstructure gradient developed as the solidification rate increased monotonically during the re-solidification process. For a laser scan velocity of 3 mm/s most of the rapid solidification microstructure is comprised of micrometer scale refined dendritic cells of α-Al(Cu) and nanometer scale refined intercellular θ-Al2Cu phase or eutectic. The cellular α-Al(Cu) constituent consistently showed Cu-solute supersaturation and a 36 % hardness increase relative to the as-cast state. The eutectic microconstituent exhibited increases in hardness that correlated quantitatively with the increasing lamellar spacing refinement obtaining for increasing solidification rate. The possible contributions from precipitation, solute and grain-size strengthening mechanisms to the hardness increase in the α-Al(Cu) cells have been assessed. The hardness increase of the α-Al(Cu) cells was attributed to a combination of solute and grain size strengthening.

Effect of Mechanical Alloying on the Dissolution of the Elemental Mn and Al-Mn Compound in Aluminum

The grain boundary, solid solution, and precipitation strengthening mechanisms are important for controlling the mechanical properties of Al-based alloys. Due to severe plastic deformation, mechanical alloying refines grain structure to a nanoscale level which leads to a strong increase in solute content and the related strengthening effect of solute atoms and secondary-phase precipitates. This study analyzed the elemental Mn and Al6Mn phase dissolution in Al during high-energy ball milling. For this purpose, XRD data, microstructure, and hardness evolutions were compared for two Al—5.2 at% Mn alloys prepared by mechanical alloying using elemental Al and Mn powders and a pre-melted master alloy. In the two-phase master alloy, containing the Al solid solution and the Al6Mn phase, the strain accumulation, grain refinement, solid solution supersaturation, and milling-induced hardening effects were facilitated. Both elemental Mn and intermetallic compound were dissolved during mechanical alloying, and the maximum solute content was near 3.1 at% Mn. A fine crystalline size of ~25 nm and the maximum Mn solute content were observed after milling of elemental powders and the master alloy for 60 h and 20 h, respectively. The microhardness of ~3 GPa corresponded to a ~3.1% solute Mn content, and the microhardness increased to ~5 GPa after long–term milling due to precipitation strengthening effect of the secondary Al6Mn phase in the master alloy.

Phase formation, microstructure evolution and strengthening mechanism of Au27.9Ag20.3Cu51.8 noble metal medium-entropy alloy during cold deformation and aging

Au27.9Ag20.3Cu51.8 noble metal medium-entropy alloy (MEA) is commercially applied in the electrical contact field due to the unique advantages, such as excellent chemical stability, outstanding electrical property and good processability. However, the low strength brings the poor deformation resistance and wear resistance in service. Herein, the cold deformation and aging treatment were applied to strengthen Au27.9Ag20.3Cu51.8 noble metal MEA, and the related evolutions of the microstructure, tensile property, and electrical resistivity were experimentally investigated. The phase formation and strengthening mechanisms were theoretically discussed. The results show that Au27.9Ag20.3Cu51.8 MEA is composed of the single-phase face-centered cubic (FCC) solid solution at the initial solution treatment of 750 °C. After the aging at 400 °C for 0.5 h, lamellar discontinuous precipitation (DP), consisting of Cu-rich and Ag-rich phases, forms at the grain boundaries (GBs), and L12-type chemical short-range order (CSRO) precipitates in both the matrix and the Cu-rich phase of DP. After 20% cold deformation, the L12-type CSRO similarly emerges in the matrix. After 20% cold deformation prior to aging at 400 °C for 0.5 h, DP at the GBs and L12-type CSRO in the matrix and the Cu-rich lamellae of DP are observed. The growth kinetics of DP and L12-type CSRO are both slightly promoted by prior cold deformation. Au27.9Ag20.3Cu51.8 MEA wire with single-phase FCC sold solution achieves the yield strength of ∼422 MPa. And, 20% cold deformation prior to aging at 400 °C for 0.5 h raises the yield strength of Au27.9Ag20.3Cu51.8 MEA wire to a peak value of ∼696 MPa. The solid solution strengthening mechanism invariably offers the largest strength contribution during the cold deformation and aging, the strain and precipitation strengthening mechanisms almost equivalently contribute to the strength improvement. The electrical resistivity maintains stable with a small variation during the cold deformation and aging. The findings in this study can provide insights for strengthening the noble metal HEAs or MEAs via traditional strengthening methods, and theoretically support for tailoring the microstructure and properties of the high-performance noble metal HEAs or MEAs.

Exploring the Impact of Cooling Rate on Microstructural Features, Mechanical Properties, and Corrosion Resistance of a Novel Nb-Stabilized Super Duplex Stainless Steel in Shielded Metal Arc Welding

The corrosion and mechanical response produced by quenching in the welded joint of a new Nb-doped stainless steel designed by the CALPHAD method and produced by open-atmosphere casting with recycled materials were investigated to contribute to the circular economy and to establish disruptive manufacturing criteria based on metallurgical principles. The steel was initially subjected to solubilization heat treatment and partial solubilization treatment at 1090 °C to obtain an appropriate α/γ balance and carbide solubilization. It was then welded by the SMAW process, quenched, and tempered at three different cooling rates. As a result, a good fit between the phases predicted by the CALPHAD method and those observed by X-ray diffraction and scanning electron microscopy were obtained, with minor differences attributable to the precipitation and diffusion kinetics required for dissolution or nucleation and growth of the phases in the system. The forced air quenching mechanism was identified as providing an α/γ phase equilibrium equivalent to 62/38 as the most effective quenching method for achieving the optimum mechanical and corrosion response, even with the post-weld σ phase and showing superior results to those of the base metal. The outstanding mechanical and corrosion responses resulted from a proper balance of the primary phases in the duplex steel with a precipitation-strengthening mechanism. The damage tolerance obtained by forced air quenching was superior to that obtained by water and air quenching, with a PSE of 24.71 GPa% post-welding.

High-strength medium-entropy alloy designed by precipitation-strengthening mechanism via machine learning

Precipitation-hardened high/medium entropy alloys (PH-HEAs/MEAs) have attracted extensive interest due to their excellent mechanical properties at both room and high temperatures. Strengthening mechanism models can be used to guide the discovery and design of new alloys, however, the parameters of the models are often lacking, limiting their use for compositional screening from a large space. We proposed a strategy combining machine learning with precipitation strengthening mechanism for high-performance PH-HEAs/MEAs. Using this strategy, we successfully synthesized an alloy Al5Ti8Co40Fe7Ni40 with a yield strength approaching 1.15 GPa, 10% higher than the best value of the existing AlTiCoCrFeNi HEAs/MEAs strengthened by L12-type nanoprecipitates. The contribution of precipitation strengthening from the L12 phase is approximately 717 MPa. Our strategy that unites the strengthening mechanism and machine learning may inspire the rapid design and discovery of precipitation-hardened alloys.

Development of a high-strength Fe–12Mn maraging steel via designing lath interfacial and intragranular nanostructures

A Heusler Fe2TiSi-phase strengthened 12Mn maraging steel Fe–12Mn–5Co–1Ti–1Mo–1Si was extensively studied using various experimental (EBSD, TEM and uniaxial tensile) techniques. The results indicate that the fine and dispersed Fe2TiSi particles, precipitating within the martensite, were the primary strengthening phase when aged at 450 °C regardless of whether the alloy is cold rolled or solid-solution treated. Furthermore, a soft reverted austenite nano-layer was observed at the lath interface, imparting significant toughness to the martensite matrix. By carefully optimizing the aging process parameters, the 12Mn alloy achieved a high tensile strength of ∼1700 MPa with a moderate elongation of ∼7% at break.When aged at 400 °C, unexpected precipitation of α-Mn particles within the martensite structure was observed, displacing the Fe2TiSi phase as the dominant strengthening phase. Simultaneously, elemental Mn segregation was found to occur at the lath interface, instead of the formation of reverted austenite. This Mn segregation layer was identified as the main factor contributing to brittle fracture behavior. These findings illustrate that synergistic improvement of strength and plasticity can be realized via an optimal combination of precipitation strengthening and interfacial layer toughening mechanisms.

Simultaneously improving strength and ductility of new-type Al–4.5Mg–2.0Zn–0.3Ag alloy by coupling of pre-deformation and non-isothermal ageing

A major challenge facing lightweight materials is the trade-off between strength and ductility. To overcome this trade-off, this study presents a new strategy that couples pre-deformation and non-isothermal ageing (NIA) of crossover Al–4.5Mg–2.0Zn‒0.3 A g alloys. Detailed evolution of microstructure and mechanical properties of the alloys under different processing routes are discussed. In this study, two different NIA thermal processing routes are employed to improve the mechanical properties of the alloy. For NC (NIA + cold rolling) technology, the post-deformation induces the accumulation of dislocations and promotes the precipitation of nanoparticles. The peak tensile strength of NC technology is 491 MPa with a poor elongation of 11.1%. For CN (cold rolling + NIA) technology, dislocation substructures, and multiscale precipitates which enhance the precipitation strengthening and work-hardening mechanisms are formed. Meanwhile, post-NIA introduces the transformation of high-density dislocations into cellular substructures and increases the dislocation storage capacity, thereby improving the ductility of the alloy. In addition, the multi-mechanistic model and strengthening mechanism are also discussed in this paper. By quantifying the increment of yield strength, the hardening effect of precipitates is superior to that of dislocations and grain boundaries. Particularly, the precipitation strengthening effect of NIA thermal processing routes is 40.8–138% higher than that of T6 technology. This study provides new ideas and a theoretical basis for developing lightweight materials with high strength and ductility.

Simultaneously improved the strength and ductility of laser powder bed fused Al-Cr-Fe-Ni-V high-entropy alloy by hot isostatic pressing: Microcrack closure and precipitation strengthening

Hot isostatic pressing (HIP) is usually applied to reduce the defects including cracks and pores in the materials prepared by laser powder bed fusion (LPBF). In the present research, in order to improve the relative density and mechanical property, HIP was employed on the LPBF-processed Al-Cr-Fe-Ni-V high-entropy alloy (HEA) with microcracks and pores. The microstructure evolution and property improvement induced by HIP were investigated. In the LPBF-processed HEA, the microcracks were caused by residual stress and element segregation, and these microcracks as well as the pores reduced significantly after HIP treatments. Remarkably, HIP temperature has a more critical effect on the microcrack closure than the holding time, thus, microcracks and pores still existed after HIP-1 treatment (1273 K, 8 h), while HIP-2 treatment (1473 K, 4 h) could close the microcracks significantly. The crack closure was attributed to the interfacial diffusion of the alloying element under high temperature accompanied by high pressure, and the degree of element diffusion at both interfaces of the cracks determined the bonding strength after crack closure. Higher temperatures at high pressure induced more adequate element diffusion and higher bonding strength. The above high temperature and high pressure also induced the growth of the L12 phase and the precipitation of the B2 phase in HEA. Consequently, the tensile strength and elongation of the LPBF-processed HEA after HIP-2 treatment were simultaneously enhanced (80.7% and 222.5% higher than that of LPBF-processed HEA, respectively). This could be attributed to the combined effect of microcrack/pore closure and precipitation strengthening. The strengthening effect of the B2 phase and L12 phase accounted for 53% (dislocation by-pass mechanism) and 47% (dislocation shearing mechanism) of the total precipitation strengthening, respectively.

Microstructural evolution and precipitation behavior of Al–7Si–3Cu alloy prepared under 5 GPa

This paper presents a systematic investigation of the microstructural evolution and mechanical properties of Al–7Si–3Cu alloys prepared under high pressure of 5 GPa. It is found that the dendritic structure disappears due to the enhanced stability of the growth interface under high pressure. Meanwhile, a considerable solute-induced modification effect is achieved in the eutectic Si. Besides, unconventional larger eutectic colonies and ultrafine nanocrystalline eutectics are observed within the intragranular area. Combined with detailed microstructural characterization, the crucial role of high pressure on the evolution of these isolated phases is discussed. The study also explores the precipitation behavior and strengthening mechanisms of alloys prepared under direct aging and solution-aging treatments. Upon the direct aging treatment, θ' phases, coarse Al2Cu particles, and Si particles form simultaneously in the matrix owing to the increased solid solubility of alloying elements, which results in the highest mechanical properties with a microhardness of 132.8 HV and compressive stress of 715 MPa. Solution-aging treatment leads to the segregation of Si on θ' phases, which proved to be energetically favorable according to first-principles calculations. This work provides new insights into the microstructural optimization of aluminum–silicon-based alloys through high-pressure manipulation and paves the way for further industrial applications.

Influence of Pre-Milling on the Mn Solid Solubility in the Al-Mn-Cu Alloy during Mechanical Alloying

Increasing the strength of Al-based alloys is an important issue of physical metallurgy and industrial processing. Severe plastic deformation and related extension of solid solubility during mechanical alloying provide an opportunity for significant strengthening due to grain refinement, solid solution, and precipitation strengthening mechanisms. During mechanical alloying, an anomalous increase in the solid-state solubility of alloying elements occurs. The present study focuses on the investigation of the pre-milling treatment to the microstructure, phase composition, and solubility in Al-7.7 Mn-3.5 Cu (wt%) alloy processed by a high-energy ball milling of Al-14.3 Mn-6.5 Cu (wt%) master alloy diluted with Al powder. During milling, the mean granular size decreased to ~5 µm, and a strong grain refinement occurred. According to our TEM and XRD data, ball milling provided a mean grain size of 13–14 nm and a microhardness of 490–540 HV. The lattice parameter of the Al-based solid solution decreased with an increase in the milling time to 7.5–10 h, which suggested the dissolution of the alloying elements, and the lattice parameter increased at a higher milling time of 12.5–40 h, which suggested the decomposition of the solid solution. The XRD data revealed the dissolution of the Al6Mn and Al20Cu2Mn3 solidification-originated phases with a further precipitation of the Al6Mn dispersoids. Pre-milling of the master alloy entailed a significant decrease in the minimal lattice parameter value from 0.4029 nm to 0.4023 nm due to an increase in the Mn solute content from 6.2 wt% (3.3 at%) to 7.5 wt % (4.0 at%) in the studied alloy during high-energy ball milling.

The microstructure characteristics and mechanical properties of Al2O3 coated TiNb fibers reinforced TiAl matrix composites

The Al2O3 coating on continuous TiNb fiber can effectively suppress the interfacial reaction in TiNbf/TiAl composites. Some phase transitions in fiber have been founded and their formation reason was analyzed. The micromechanical properties of each phase and macroscopic mechanical properties of the composites were also systematically studied. The α+β duplex structure exhibiting texture feature was found in the most regions of TiNb fiber. Meanwhile α+δ layer, σ layer, outer α layer, and β layer would be formed respectively within 10 μm of the fiber surface whose formation reasons were explained from thermodynamics dominated by Al element. Nanoindentation tests indicated the deformation capacity of each phase satisfied: β＞δ＞σ＞α (outer)＞α (inner)＞Al2O3 coating. The composite with coated fibers has excellent fracture strength of 498 MPa and the fracture toughness of 18.72 MPa m, which was benefited from the fine grain strengthening and precipitation strengthening mechanisms. The Al2O3 coating can significantly improve the thermal stability of the composites during thermal exposure below 1250 °C, and keep the mechanical properties from degradation. This work is of great significance for understanding the phase transformation and deformation process of innovative Al2O3 coated TiNb fiber reinforced TiAl matrix composites.

Effect of Al–5Ti–0.3C–0.2B Master Alloy on the Structure and Properties of Ti6Al4V by Laser Solid Forming

Titanium matrix composites (TMCs) with the addition of in situ ceramic reinforcing particulates have attracted extensive interest. Herein, additive‐manufactured Ti6Al4V/Al–5Ti–0.3C–0.2B alloys are fabricated from mixed powders by laser solid forming. The contents of Al–5Ti–0.3C–0.2B with 1.5, 2.5, and 5.0 wt% are considered. The results indicate the apparent microstructure transition from columnar grain to equiaxed grain with increasing content of Al–5Ti–0.3C–0.2B. The in situ reaction between the Ti6Al4V and Al–5Ti–0.3C–0.2B produces TiB, TiC, and Ti3AlC reinforcements. The increase of Al–5Ti–0.3C–0.2B content will refine grains and reduce α′ martensite phase, which is associated with the formation of TiB at the grain boundaries. As the content of Al–5Ti–0.3C–0.2B increases, the ultimate tensile strength of Ti6Al4V–x wt% (Al–5Ti–0.3C–0.2B) alloy increases from 993.8 MPa to 1233.6 MPa. The strength increases because of an increase of the solid phases TiB and Ti3AlC, which is ascribed to the presence of precipitation and grain refinement strengthening mechanisms. Meanwhile, the elongation of the alloy increases from 1.1% to 4.9% because the Ti3AlC phase is conducive to reducing thermal transfer and interfacial stress. These findings provide insights into the selection of reinforcement materials for optimizing mechanical properties of TMCs alloys.

Strengthening of CoCrNi medium entropy alloy with gadolinium additions

A series of (CoCrNi)100–xGdx (x = 0/0.1/0.3/0.5/1.0) medium entropy alloys (MEAs) was fabricated by high-vacuum arc melting. The effects of rare-earth element, Gd, additions on the evolution of microstructures and mechanical properties of CoCrNi MEAs were studied. The phase and microstructure were examined using X-ray diffraction, scanning electron microscope and transmission electron microscope. The tensile properties were measured by material testing system (MTS) and the hardness was measured by both Vickers indenter and nanoindentation. As the Gd concentration increased, the phase transformed from face-centered cubic (FCC) to hexagonal close-packed (HCP) precipitates in FCC matrix. Compared to the single phase CoCrNi MEA with the yield strength of 400 MPa and fracture strength of 880 MPa, CoCrNi99.5Gd0.5 MEA exhibited a much higher yield strength of 751 MPa and ultimate tensile strength of 1216 MPa, while the ductility still maintained a high value of ∼55%. The enhanced mechanical properties were ascribed to solid solution, precipitation and grain refinement strengthening mechanisms. The relations among compositions, microstructures and mechanical properties of (CoCrNi)100–xGdx MEAs were discussed.

Microstructural, thermal and mechanical properties of Co added Sn–0.7Cu lead-free solder alloy

This study investigated the effects of cobalt microalloying addition on the microstructural features, thermal characteristics and mechanical behavior of eutectic Sn–0.7wt%Cu lead-free solder alloys. The results show that minor cobalt addition of ~ 0.05 wt% causes significant grain refinement of β-Sn, facilitates the formation of fine fibers (Cu,Co)6Sn5 phases and preventing the formation of η′-Cu6Sn5 phases, whereas a large amount of Co (~ 0.5 wt%) additions accumulated in the (Cu,Co)6Sn5 IMCs and clearly changed into coarse fibers. The precipitation strengthening mechanisms of fine fibers (Cu,Co)6Sn5 in the β-Sn matrix increased the ultimate tensile strength (UTS) and Young’s modulus (Y) of the alloy from 30.5 MPa and 15 GPa to 44.6 MPa and 22.3 GPa, respectively, but the ductility decreased from 60 to 45.7%. The coarse fibers (Cu,Co)6Sn5 in eutectic alloys is of interest from not only increased UTS and Y to 38.7 MPa and 16.3 GPa but also maintaining the ductility at the same level, allowing for unique microstructure design. Furthermore, 0.05wt% of Co significantly reduce the onset, eutectic temperatures and undercooling, although pasty rang has been slightly raised, which may enhance the thermal characteristics. This presumably has important implications for the reliability of solders as well as their performance in electronic service.

Precipitation behaviour and strengthening mechanisms of V-bearing 1800 MPa grade hot-stamping steel

Achieving strength-ductility synergy of hot-stamping steel via microalloying technology has attracted great attention due to their pronounced precipitation strengthening. Nevertheless, the precipitation behaviours and characteristics have not been clearly unveiled. In this work, the effects of V content on the microstructure and mechanical properties of 1800 MPa grade hot-stamping steel are systematically studied. Massive V contained precipitates develop after hot-rolling and coiling, which refine the martensitic microstructure and retain in the matrix after austenitizing and quenching. The refined martensite with massive precipitates is responsible for the good mechanical properties. Generally, the tensile strength decreases slightly with increasing V content from 0.04% to 0.2%, as V consumes C in the martensite matrix by forming carbides and promoting precipitate coarsening.

Mechanical Properties of Internally Hierarchical Multiphase Lattices Inspired by Precipitation Strengthening Mechanisms.

In metal metallurgy, precipitation strengthening is widely used to increase material strength by utilizing the impediment effect of the second-phase particles on dislocation movements. Inspired by this mechanism, in this paper, novel multiphase heterogeneous lattice materials are developed with enhanced mechanical properties utilizing a similar hindering effect of second-phase lattice cells on the shear band propagation. For this purpose, biphase and triphase lattice samples are fabricated using high-speed multi jet fusion (MJF) and digital light processing (DLP) additive manufacturing techniques, and a parametric study is carried out to investigate their mechanical properties. Different from the conventional random distribution, the second-phase and third-phase cells in this work are continuously distributed along the regular pattern of a larger-scale lattice to form internal hierarchical lattice structures. The results show that the triphase lattices possess balanced mechanical properties. Interestingly, this indicates that introducing a relatively weak phase also has the potential to improve the stiffness and plateau stress, which is distinct from the common mixed rule. This work is aimed at providing new references for the heterogeneous lattice design with outstanding mechanical properties through material microstructure inspiration.