Three common structural characteristics of natural armor materials and their strengthening and toughening related intrinsic mechanism were summarized, and three typical biomechanical effects, including gradient structure orientation effect, in-situ structure reorientation effect and multistage "suture" interface effect were also summarized, and the corresponding structural optimization design principles of biomimetic materials were proposed. The constant improvement of biomechanics theory and the comprehensive application of various biomimetic structures are beneficial to solve practical engineering problems with new biomimetic materials.
The films of corundum structure Al2O3 were successfully deposited on gold foil with pre-deposited α-Al2O3 seeds at low-temperature by reactive RF (Radio Frequency) sputtering with Al+α-Al2O3(15% α-Al2O3) target. The surface morphology, phase constituent and chemical composition of the as-deposited films were characterized by SEM, GIXRD and EDS. Results show that films of single α-Al2O3 with corundum-like crystallographic structure could be deposited at 560℃ on Si(100) substrate by reactive sputtering with Al+α-Al2O3 as composite target, while the substrate temperature even could be reduced to 500℃ for gold foil with pre-deposited α-Al2O3 seeds (the density of α-Al2O3 seeds is ~106/cm2) by reactive sputtering with pure Al as target. The results of the above two deposition methods proved that α-Al2O3 seeds may be favorable for the deposition of single phase α-Al2O3 films on the substrate at lower temperature.
The microstructure and mechanical properties of extruded Mg-alloy of Mg-1Al-0.4Ca-0.5Mn-0.2Zn (mass fraction, %) were systematically investigated. As indicated by the results, the incomplete dynamic recrystallization occurred for the alloys extruded at 260℃ (denoted as AXMZ1000-260) and 290°C (AXMZ1000-290) with recrystallized grain sizes of 0.75 μm and 1.2 μm, respectively. The two alloys have high-density G.P. regions and spherical nano-phases, which can effectively inhibit the dislocation motion and provide abundant nucleation sites for dynamic recrystallization. Moreover, the nano-phases precipitated along grain boundaries can restrain the migration of grain boundary and restrict the growth of DRXed grains, which results in the ultrafine grains with a size of 0.75 μm in AXMZ1000-260 alloy. The strength of the alloy decreases with the increase of extrusion temperature, and the change of elongation is not obvious. The yield strength and elongation of alloys extruded at 260℃ and 290℃ are approximately 322 MPa and 343 MPa, as well as 13.4% and 13%, respectively. The dynamic precipitation and recovery process are promoted by the increasing extrusion temperature, and a high-density G.P. zones and spherical nano-phases are accumulated in the alloy. At the same time, many dislocations are transformed into LAGBs by dynamic recovery, and the unDRXed areas are subdivided into dense lamellar subgrains. The nano-phases and LAGBs can effectively hinder the newly generated dislocation motion, which is the major reason that the alloy extruded at 290℃ still have a high yield strength and the change of ductility is not obvious. Furthermore, TEM observations show that the pinning effect of G.P. zones can impede the dynamic recovery to certain extent, resulting in a high number of residual dislocations in the alloy, which is conducive to the improvement of the yield strength.
The effect of austenitizing temperature on the microstructure evolution and low temperature toughness of high strength low alloy (HSLA) steel was investigated by OM and SEM. The results show that with the increase of austenitizing temperature from 850℃ to 950℃ while heat treated for 30 min, the average austenite grain size increases from 7.22 μm to 17.39 μm (the temperature of AC3 is 819℃). After quenching at 850~950℃, the microstructure is lath martensite. The yield strength and tensile strength decreased respectively, and there was no obvious variation in elongation. However, the toughness decreased significantly from 97 J to 31 J. The crystallographic analysis results by EBSD and ARPGE software show that the grain size increased and the variants selection enhanced with the increase of quenching temperature, which show that austenite grain is mainly occupied by a single pair of variants. In addition, the combination mode of the variants for the 850A sample tends to show a CP (Close packed) combination mode. When the austenitizing temperature increased to 950℃, the combination mode of the variants is more likely to be Bain group combination, and the proportion of operation factors representing high angle misorientation decreases, which leads to the decrease of high angle grain boundary density, and the ability to hinder crack propagation is reduced, further deteriorating the impact toughness.
The composite of hollow carbon/Fe3O4 magnetic quantum dots (C/MQDs) was synthesized via in-situ polymerization-solvothermal-calcination process with silicon dioxide as the template. The morphology, crystallographic structure, chemical composition, intrinsic structural defects, relative graphitization degree and electromagnetic parameters of the prepared composite C/MQDs were characterized by means of SEM, TEM, Raman spectroscopy, XRD, XPS and Vector network analyzer (VNA) etc. It follows that electromagnetic parameters of the prepared C/MQDs could be adjusted by changing the addition amount of ferric nitrate so that to adjust its microwave absorption (MA) performance. In fact, a hollow ring made of the mixed composite and paraffin with 7 mm in outer diameter and 2.55 mm in thickness presented a maximum effective absorption bandwidth (EAB) of 7.06 GHz and a minimum reflection loss value (RLmin) of -43 dB. The excellent microwave absorption performance of the prepared composite is mainly derived from its electromagnetic matching characteristics and the synergistic effect of dielectric-magnetic loss.
Hydroxyapatite (HA)-barium titanate (BT) of human bone imitating composite material was prepared by sintering process with HA powder and BT powder as raw material，and then was characterized by XRD, SEM with EDS, synchronous thermal analyzer, universal material testing machine, quasi-static piezoelectric coefficient measuring instrument and dielectric constant measuring instrument. The results show: the partial decomposition of HA and BT resulted in the reaction of the raw materials in the pressed block at certain temperature to produce CaTiO3, Ca3(PO4)2, TiO2, BaTi2O5 and other phases. The bio-piezoelectric HA-BT composite containing 70% BT sintered at 1200℃ is composed of grains uniform size with good compactness and comprehensive property closed to those of human bone, such as compressive strength (110.215 MPa) and electrical properties (d33=2 pC/N, εr=44.6).
Er2O3 doped ceramic materials (Gd1-xErx)2(Zr0.8Ti0.2)2O7 (x=0, 0.2,0.4, x is mole fraction) were prepared by solid-state reaction method, the crystallographic structure, microstructure, thermophysical properties and mechanical properties of the materials were examined in terms of the effect of Er2O3 doping. The results show that (Gd1-xErx)2(Zr0.8Ti0.2)2O7 ceramic material presents the same crystallographic structure as cubic pyroclase with good high temperature phase stability from room temperature to 1200℃. Er3+ doping can reduce the thermal conductivity and the average thermal expansion coefficient of the ceramic materials, peculiarly, the thermal conductivity of (Gd0.8Er0.2)2(Zr0.8Ti0.2)2O7 ceramic material is the lowest at 1000℃, which is 1.26 W·m-1·k-1. In addition, the doping of Er3+ can improve the hardness and fracture toughness of the material.
A series of (CrTiAl)N hard films with the same morphology and thickness but different Al/Ti molar ratio were prepared via multi-arc ion plating technology with desired processing parameters while varying the combination mode of cathode arc source and target. The chemical composition, microstructure, phase constituent and surface hardness of the films were characterized. Meanwhile the effect of Al/Ti molar ratio on the phase structure and hardness of the films were investigated. The results show that：the (CrTiAl)N films with different Al/Ti molar ratios present the same phase constituents with preferred growth orientations (200) and (111). With the increase of Al/Ti molar ratio from 0.38 to 0.85, the hardness of the film shows a regular change. The hardness of (CrTiAl)N films with Al/Ti molar ratio of 0.49 is the highest, reaching HV4200, however when the Al/Ti molar ratio is 0.85, the hardness decreases to HV2600. The Al/Ti molar ratio has a direct effect on the hardness of the film and shows a non-monotonic relationship when the microstructure, thickness and CrN content of the films are basically unchanged. In the larger Al/Ti molar ratio range, the phase structure of (CrTiAl)N films is unchanged and all of them are displacement-centered cubic solid solutions. The hardness of (CrTiAl)N films is significantly higher than that of (CrTiN) films and which can possess super hardness by optimizing the molar ratio of Al/Ti.
The composite coating of Ti2Ni+TiC+Al2O3+CrxSy was laser cladded on the surface of Ti811 alloy via coaxial powder feeding technology with mixed powders TC4+Ni45+Al2O3+MoS2+Y2O3 as cladding material. The microstructure, microhardness, friction and wear properties of the coating were characterized by means of SEM, EDS, XRD, microhardness tester and friction tester. The results show that the Ni and C of Ti811 alloy react with Ti respectively during laser cladding, so that the intermetallic compound Ti2Ni and hard reinforced phase TiC can form in situ, while the soft lubrication phase CrxSy also formed due to the sulfurization reaction between S and Cr after the decomposition of MoS2. The Ti2Ni-phase may present as network-like, TiC as spheroidal and dendritic, while Al2O3 as punctiform, which all uniformly distributed in the clad coating. The combined action of strengthening of the hard phase and lubrication of the soft phase makes the laser clad coating with higher microhardness and better wear resistance. When the laser power is 900W the average microhardness of the clad coating reaches 1303.5HV0.5 with the best wear resistance.
Maleic anhydride (MAH) grafted polylactic acid (PLA), namely MPLA was made via melting reaction method. Then reactive compatilizer ESO-G-(MAH-co-PLA) (ECP) was further prepared via chemical graft of epoxidized soybean oil (ESO) and MPLA.The prepared ECP was characterized by FT-IR, DSC and SEM. The influence of four different feeding methods and mole ratio between ESO and MAH on graft rate and acid value of ECP was investigated. The results show that during the MPLA preparation stage, 1/3 of the desired amount ESO was added first, and subsequently the remaining 2/3 of ESO and all triethylamine were added at the chemical graft stage, as a result the grafting rate of ECP was up to 4.1514%；When the mole ratio of ESO to MAH group is 1, the grafting effect of products is the best. The PLA material modified with ECP has better comprehensive performance than the one with ESO. The addition of ECP can improve the hydrophobic performance of PLA.
