Improving mechanical properties and high-temperature oxidation of press hardened steel by adding Cr and Si

This work investigated the effect of Cr and Si on the mechanical properties and oxidation resistance of press hardened steel.Results indicated that the microstructure of the Cr-Si micro-alloyed press hardened steel consisted of lath martensite,M_(23)C_(6)carbides,and retained austenite.The retained austenite and carbides are responsible for the increase in elongation of the micro-alloyed steel.In addition,after oxidation at 930℃for 5 min,the thickness of the oxide scales on the Cr-Si micro-alloyed press hardened steel is less than 5μm,much thinner than 45.50μm-thick oxide scales on 22MnB5.The oxide scales of the Cr-Si micro-alloyed steel are composed of Fe_(2)O_(3),Fe_(3)O_(4),mixed spinel oxide(FeCr_(2)O_(4)and Fe_(2)SiO_(4)),and amorphous SiO_(2).Adding Cr and Si significantly reduces the thickness of the oxide scales and prevents the generation of the FeO phase.Due to the increase of spinel FeCr_(2)O_(4)and Fe_(2)SiO_(4)phase in the inner oxide scale and the amorphous SiO_(2)close to the substrate,the oxidation resistance of the Cr-Si micro-alloyed press hardened steel is improved.

Simple shear extrusion versus equal channel angular pressing:A comparative study on the microstructure and mechanical properties of an Mg alloy

Two severe plastic deformation(SPD)techniques of simple shear extrusion(SSE)and equal channel angular pressing(ECAP)were employed to process an extruded Mg-6Gd-3Y-1.5Ag(wt%)alloy at 553 K for 1,2,4 and 6 passes.The microstructural evolutions were studied by electron back scattered diffraction(EBSD)analysis and transmission electron microscopy(TEM).The initial grain size of 7.5μm in the extruded alloy was reduced to about 1.3μm after 6 SPD passes.Discontinuous dynamic recrystallization was suggested to be operative in both SSE and ECAP,with also a potential contribution of continuous dynamic recrystallization at the early stages of deformation.The difference in the shear strain paths of the two SPD techniques caused different progression rate of dynamic recrystallization(DRX),so that the alloys processed by ECAP exhibited higher fractions of recrystallization and high angle grain boundaries(HAGBs).It was revealed that crystallographic texture was also significantly influenced by the difference in the strain paths of the two SPD methods,where dissimilar basal plane texture components were obtained.The compression tests,performed along extrusion direction(ED),indicated that the compressive yield stress(CYS)and ultimate compressive strength(UCS)of the alloys after both SEE and ECAP augmented continuously by increasing the number of passes.ECAP-processed alloys had lower values of CYS and UCS compared to their counterparts processed by SSE.This difference in the mechanical responses was attributed to the different configurations of basal planes with respect to the loading direction(ED)of each SPD technique.

Microstructure and mechanical properties of Mg-Gd-Y-Zr alloy processed by equal channel angular pressing

Microstructure evolution and texture development and their effects on mechanical properties of a Mg-Gd-Y-Zr alloy during equal channel angular pressing（ECAP） were investigated.It is found that the microstructure is still inhomogeneous after four passes,and two zones,namely the fine grain zone（FGZ） and the coarse grain zone（CGZ） are formed.The grain refinement occurs mainly by particle-stimulated nucleation（PSN） mechanism,which led to a more random texture after four passes of ECAP.In the ECAP-processed alloy,the strength did not increase while the ductility was enhanced dramatically compared with the as-received condition.The change of ductility of this alloy was discussed in terms of texture and second phase particles.

Effect of consolidation parameters on mechanical properties of Cu-based bulk amorphous alloy consolidated by hot pressing

Cu50Zr40Ti10 bulk amorphous alloys were fabricated by hot pressing gas-atomized Cu50Zr40Ti10 amorphous powder under different consolidation conditions without vacuum and inert gas protection. The consolidation conditions of the Cu50Zr40Ti10 amorphous powder were investigated based on an L9（34） orthogonal design. The compression strength and strain limit of the Cu50Zr40Ti10 bulk amorphous alloys can reach up to 1090.4 MPa and 11.9 %, respectively. The consolidation pressure significantly influences the strain limit and compression strength of the compact. But the mechanical properties are not significantly influenced by the consolidation temperature. In addition, the preforming pressure significantly influences not the compression strength but the strain limit. The optimum consolidation condition for the Cu50Zr40Ti10 amorphous powder is first precompacted under the pressure of 150 MPa, and then consolidated under the pressure of 450 MPa and the temperature of 380 °C.

Microstructures and mechanical properties of 2024Al/Gr/SiC hybrid composites fabricated by vacuum hot pressing

The 2024Al/Gr/SiC hybrid composite plates with 5%-10% SiC particles （volume fraction） and 3%-6% flaky graphite （Gr） （volume fraction） were fabricated by vacuum hot pressing and hot extrusion processing. The effects of SiC and Gr on the microstructures and mechanical properties of the composites aged at 160, 175 and 190℃ were studied by optical microscopy, scanning electron microscopy （SEM）, and hardness and tensile tests. The results indicate that the SiC particles have a more obvious effect on accelerating the aging response as compared with the Gr. Both the tensile strength and elongation are reduced by the Gr and SiC particles added into the matrix, while the Gr has a more negative influence on the elongation than the SiC particles. The tensile strength （ab）, yield stress （as） and elongation （δ） of the 2024Al/3Gr/10SiC composite aged at 165℃ for 8 h are 387 MPa, 280.3 MPa and 5.7%, respectively. The hybrid composites are characterized by ductile fracture, which is associated with the ductile fracture of the matrix and the tearing of the interface between the matrix and the particles.

Design of a Servo Mechanical Press with Redundant Actuation

A servo press is a new type of mechanical press that is driven by programmable motors and offers superior performance such as low noise, excellent efficiency and high precision for metal forming operations. Similar to multi-link mechanical presses, a servo mechanical press tends to grow in size as the tonnage increases that calls for larger, heavy duty servo motors, which could be expensive and may not even be available. In this paper, a new concept of servo mechanical press with redundant actuation is proposed firstly using two servo motors driving one input shaft, i.e. one-point-two-motor mode that makes it possible to produce a larger press with available servomotors. Then the punching mechanism design is detailed. The performance indices are set up including mechanical advantage reciprocal and link force ratios. A bounded feasible solution space is constructed for dimensional synthesis based on non-dimensional link lengths and assembly conditions. The performance atlases are depicted over the bounded feasible solution space that lead to a visual solution of the punching mechanism with global optimization. Finally, case studies are given to illustrate the design method with visual global optimization, and a prototype with 200 t punching force is being developed in our laboratory to demonstrate efficacy of the new concept for servo mechanical press. The presented research provides a feasible solution to the development of heavy-duty servo mechanical presses and finds potential applications in the development of other types of heavy equipments with electric drive.

Effect of Y content and equal channel angular pressing on the microstructure, texture and mechanical property of extruded Mg-Y alloys

The microstructure, texture and mechanical property evolution of the extruded Mg-x Y(x = 1, 5 wt.%) alloys during equal channel angular pressing(ECAP) were systematically investigated using an optical microscope, electron backscatter diffraction(EBSD) and uniaxial tensile test. The Mg-Y alloys exhibited a weakened basal texture before the ECAP, and the texture was further weakened with the max basal poles dispersed along ~45° between the extrusion direction and the transverse direction after the ECAP. The Mg-5 Y alloys always exhibited a finer grain size comparing to that of Mg-1 Y for the same ECAP process. With a proper ECAP process, both the strength and elongation of Mg-5 Y alloy could be improved simultaneously after the ECAP, i.e., the yield strength(273.9 ± 1.2 MPa), ultimate strength(306.4 ± 3.0 MPa),and elongation(23.9 ± 1.0%) were increased by 10%, 6%, and 72%, respectively, comparing to that before the ECAP. This was considered to be arose from the combined effects of grain refinement, significant improved microstructure homogeneity and solid solution hardening.In addition, it was found that Mg-Y alloy with better comprehensive properties could be obtained by the decreasing-temperature ECAP processes. The yield strength-grain size relationship could be well described by the Hall-Petch relation for all the ECAPed Mg-Y alloys,which was consistent with that the texture changes did not significantly affect the average Schmid factors of basal, prismatic and pyramidal slips for both Mg-Y alloys.

Microstructure and mechanical properties of ZE10 magnesium alloy prepared by equal channel angular pressing

ZE10 magnesium alloy was subjected to equal-channel angular pressing （ECAP） up to 12 passes in a die with an angle of 120° between the two channels at 250-300℃. An inhomogeneous microstructure of bimodal grains including fine grains of 1-2 μm as well as coarse grains of about 20μm was obtained after the initial 1-4 ECAP passes. The grain size became increasingly homogeneous with further ECAP processing and the grains were significantly refined to 1-2 ktm after 8 passes and further refined to 0.5-1 μm after 12 passes. The alloy＇s yield strength changed slightly but the ductility improved greatly initially up to 4-6 passes corresponding to the bimodal grain microstructure. And after the subsequent pressing of more than 8 passes, the tensile strength including yield strength improved while the elongation decreased gradually.

Mechanical and wear properties of Al-Al_3Mg_2 nanocomposites prepared by mechanical milling and hot pressing

β-A13Mg2 intermetallic was used as a reinforcing agent to improve the mechanical properties of an aluminum matrix. Different amounts of A13Mg2 nanoparticles （ranging from 0wt% to 20wt%） were milled with aluminum powders in a planetary ball mill for 10 h. Consolidation was conducted by uniaxial pressing at 400β under a pressure of 600 MPa for 2 h. Microstructural characterization confirms the uniform distribution of A13Mg2 nanoparticles within the matrix. The effects of nano-sized A13Mg2 content on the wear and mechanical properties of the composites were also investigated. The results show that as the A13Mg2 content increases to higher levels, the hardness, compressive strength, and wear resistance of the nanocomposites increase significantly, whereas the relative density and ductility decrease. Scanning electron microscopy （SEM） analysis of worn surfaces reveals that a transition in wear mechanisms occurs from delamination to abrasive wear by the addition of A13Mg2 nanoparticles to the matrix.

Reconstruction of impact force of mechanical press in time domain

To overcome the difficulty in directly measuring the impact force of a mechanical press, the inverse theory is employed to reconstruct the impact force from the corresponding response data in time domain. The nature of ill-posedness of impact force reconstruction is explored through singular value decomposition （SVD） and the Tikhonov regularization is utilized to deal with the ill-posedness, in which the optimal parameter is chosen in light of the L-curve criterion and the generalized cross- validation （GCV）. The experimentally measured strain responses of upper and lower dies of the press are chosen as source data for impact force reconstruction, and the corresponding numerical results are compared with the experimental measurements, which verifies the effectiveness of the reconstruction method.

Microstructure,Mechanical,and Thermal Properties of B4C-TiB2-SiC Composites Prepared by Reactive Hot-pressing

B4C-TiB2-SiC composites with excellent properties were prepared by reactive hot-pressing using B4C,TiC,and Si powders as the raw materials.The phase transition process was investigated by heating the powder mixture to different temperatures and combined with XRD tests.TiB2 and SiC phases were synthesized through an in situ reaction,and the mechanical and thermal properties were improved simultaneously.Microstructure and mechanical properties were also studied,and the 60wt% B4C-21.6wt% TiB2-18.4wt% SiC composite showed a relative density of 99.1%,Vickers hardness of 34.6 GPa,flexural strength of 582 MPa,and fracture toughness of 5.08 MPa·m1/2.In addition,the values of thermal conductivity and thermal expansion coefficient were investigated,respectively.

Enhancing mechanical properties and corrosion performance of AA6063 aluminum alloys through constrained groove pressing technique

The use of a constrained groove pressing(CGP) method to plastically deform AA6063 aluminum alloy led to the improved surface properties. It was found that hardness magnitude is dramatically improved and its uniformity is considerably decreased after the first pass, while subsequent passes result in better hardness behavior for the processed material. Also, the elongated grains formed in the first pass of the CGP are gradually converted to the equiaxed counterparts by adding pass numbers. Eventually, higher corrosion resistance of the sample by imposing the CGP process is related to the quick formation of passivation film and the change in the morphology of the second phase and precipitates which hinder their electrochemical reactions and decrease the potential localized attack sites.

Microstructure and Mechanical Properties of Ultrafine Grained Mg15Al Alloy Processed by Equal-channel Angular Pressing

An as-cast magnesium alloy with high Al content Mg15Al was subjected to equal-channel angular pressing （ECAP） through a die with an angle of φ= 90？ at 553 K following route Bc. It is found that the network β-Mg17Al12 phases in the as-cast Mg15Al alloy are broken into small blocks and dispersed uniformly with increasing numbers of pressing passes. Moreover, many nano-sized Mg17Al12 particles precipitate in the ultra-fine α-Mg matrix. The grains are obviously refined. However, the grain structure is inhomogeneous in different areas of the alloy. The average size of the primary phase α-Mg is reduced to about 1 μm while grains of around 0.1-0.2 μm are obtained in some two-phase areas. With additional ECAP passes （up to 8）, coarsening of the grains occurs by dynamic recovery. Room temperature tensile tests show that the mechanical properties of Mg15Al alloys are markedly improved after 4 ECAP passes. The ultimate tensile strength and elongation to failure increase from 150 MPa to 269.3 MPa and from 0.05% to 7.4%, respectively. Compared with that after 4 passes, the elongation to failure of the alloy increases but the strength of the alloy slightly decreases after 8 ECAP passes. Fracture morphology of the ECAP-processed alloy exhibits dimple-like fracture characteristics while the as-cast alloy shows quasi-cleavage fractures.

Research on Hybrid Input Mechanical Press Driven by Two Motors

Given the speed requirements of a mechanical press slider, a differential gear train is adopted instead of the belt and gear drive of a general mechanical press. Two electric motors are used to drive the differential gear train with hybrid input. Based on the working principle of a differential gear train, the angular speed equations and the power dis- tribution equations of the input-output system are established. By controlling the angular speeds of the two motors, the slider can move at different speeds. Taken a JH23-100 type mechanical press as example, the driving system is designed and the power of two motors determined. The simulated results show that the highest slider speed in the mechanical press approaches 39 mm/s only at the forging-punching stage, far less than the 232 mm/s of a general JH23-100 type mechanical press. This provides a new scheme to realize low-speed forging-punching technology from a mechanical press.

Transformation of Fibrous Membranes from Opaque to Transparent under Mechanical Pressing

There is a great demand for transparent films,membranes,or substrates in the fields of intelligent wearables,electronic skins,air filtration,and tissue engineering.Traditional materials such as glass and plastics cannot satisfy these requirements because of the lack of interconnected pores,undesirable porosity,and flexibility.Electrospun fibrous membranes offset these shortcomings because they contain small pores and have high porosity as well as outstanding flexibility.Thus,the development of transparent electrospun fibrous membranes is of great value.This work reports a simple and effective way to develop flexible and porous transparent fibrous membranes(TFMs)directly from electrospun fibrous membranes via mechanical pressing,without employing any other additives.In addition,the relationship between the transparency performance and the molecular structure of the polymers after pressing was summarized for the first time.After mechanical pressing,the membranes maintained fibrous morphology,micron-sized pores,and desired porosity.Polystyrene fibrous membranes,which exhibited excellent optical and mechanical properties,were used as a reference.The TFMs possessed high transparency(~89%visible light transmittance at 550 nm),high porosity(10%–30%),and strong mechanical tensile strength(~148 MPa),nearly 78 times that of the pristine electrospun fibrous membranes.Moreover,this study demonstrated that transparent and conductive membranes can be fabricated based on TFMs using vacuum-assisted filtration of silver nanowires followed by mechanical pressing.Compared with indium tin oxide films,conductive TFMs exhibited good electrical conductivities(9Ωper square(Ω·sq^(−1)),78%transmittance at 550 nm)and notable mechanical performance(to bear abundant bending stresses).

Synthesis of Ti_2AlC by hot pressing and its mechanical and electrical properties

Ti2AlC bulk material was synthesized by hot pressing of mixture powders of TiC, Ti, Al and active carbon. The phase compositions of resultant product at different temperature were detected by X-ray diffractometer. The microstructures of the samples were observed by SEM. Finally, the mechanical properties and thermal properties of the sample at 1400 ℃ were measured. The results show that high purity Ti2AlC material with little Ti3AlC2 can be synthesized by hot pressing 0.5TiC/1.5Ti/1.0Al/0.5C at 1 400 ℃. Ti2AlC exhibits high mechanical properties and metallic electrical properties. Its fracture toughness is 7.0 MPa·m1/2, its flexural strength is 384 MPa at room temperature, and its electrical conductivity is 2.56×106 Ω1·m-1 at room temperature.

Effects of TiB2 Content on the Microstructures and Mechanical Properties of Low-Cobalt Ti（C,N）-TiB2 Cermets Fabricated by Vacuum Hot Pressing

Ti(C,N)-TiB2 cermets were fabricated from Ti(C,N), TiB2, Co and WC powder mixtures via a vacuum hot pressing process. The influence of TiB2 content on their microstructures and mechanical properties was investigated. As a result of the elevated TiB2 contents, two types of corerim microstructures were present in the Ti(C,N)-TiB2 cermets, and remarkably improved mechanical properties were achieved. With the increase of TiB2 content, the flexural strength, fracture toughness and hardness of the Ti(C,N)-TiB2 cermets first increased, and then decreased, while their relative density consistently decreased. Attributed to an integration of the intergranular and intrangranular fracture behaviors, the Ti(C,N)-TiB2 cermets with 20 wt% TiB2 content exhibited the best overall properties with the relative density, hardness, fracture toughness and flexural strength at 99.3%, 1 995 HV, 7.92 MPa·m1/2 and 1 114 MPa, respectively. The underlying mechanism for their enhanced properties was studied in detail.

Mechanical properties and microstructure of in situ TiB_2/Cu composite fabricated by reactive hot pressing

A copper matrix composite reinforced by TiB_2 particle was fabricated by reactions of Cu,Ti and B powders.The microstructure and mechanical properties of the in situ composite were investigated.The results showed that the in situ formed TiB_2 particles,which has a size of no larger than 1 μm,exhibits a uniform distribution in the copper matrix.Due to TiB_2 reinforcement,the mechanical properties in terms of Young's modulus and yield and ultimate tensile stress of the in situ TiB_2/Cu composite are improved greatly.In addition,even if the volume fraction of TiB_2 reinforcement are the same,the composite in the present study containing fine TiB_2 particles exhibits much higher properties than that of the composite reinforced with coarse ones.

Synthesis of TiAl based alloy by mechanical milling, warm pressing and reactive sintering

The synthesis process TiAl based alloy by mechanical milling, warm pressing and reactive sintering was investigated. The microstructure of Ti-Al mixture powders milled was analyzed by backscattering electron image （BSE）. Then, the powders were warmly pressed in a vacuum hot-pressing device and reactively sintered at different temperatures for different times, the microstructures of TiAl based alloys after sintering were analyzed by scanning electron microscopy（SEM）, energy dispersive spectroscopy（EDS） and optical microscopy（OM）. The compositions of all stages were also analyzed by X-ray diffraction（XRD）. The results show that warm pressing can increase the relative densities of Ti-Al powder billets obviously. The billets warmly pressed with high relative density can be transformed into near fully-densified TiAl based alloy through pre-sintering at low temperature and sintering at high temperature for appropriate time, and the microstructure of the TiAl based alloy is the typical lamellar structure composed of γ-TiAl and α2-Ti3Al.

Mechanical Properties of the Cured Laminates on the Hot-press Tackified Preforms in Vacuum Assisted Resin Transfer Molding

A hot-press tackified preform was used to improve the uniformity of the laminates thickness and the mechanical properties of the obtained laminates were studied using vacuum assisted resin transfer molding（VARTM）. Two modified preforms were prepared under 0.1 and 0.6 MPa in an autoclave and then were used to fabricate the laminates via VARTM. Permeability and thickness distribution of the laminates were obtained by using a special device. Moreover, the tensile and compressive strengths of the obtained laminates were studied and compared with the unmodified ones. Results show that the tackified laminates present a maximum and minimum thickness under 0.1 and 0.6 MPa, respectively. The thicknesses and in-plane permeability of the tackified laminates, with better thickness uniformity, are significantly decreased compared with that of the unmodified cases, while the tensile and compressive strengths of the tackified laminates are improved obviously. Results show that the mechanical property of the tackified laminates prepared by hotpressing at 0.1 MPa is better than that processed at 0.6 MPa.