High Level Of Mechanical Properties Research Articles

Development of multi-cycle quenching–partitioning–tempering process and its applications in engineering

AbstractQuenching–partitioning–tempering (Q–P–T) steels have become a new member of the family of advanced high strength steels. Previous research indicates that steels treated by the Q–P–T process exhibit better combinations of strength and elongation than those treated by traditional quenching and tempering (QT this has been attributed to the lower quenching stress and larger amount of retained austenite in the Q–P–T steels. In the present paper, the concept of water–air alternately timed quenching (ATQ) technology, in effect a multi-cycle Q–P–T (MQ–P–T) process, is presented. The principles of ATQ technology and related equipment are introduced. Examples given of workpieces treated by ATQ technology include a 718 steel plastic die, a 42CrMo4 marine crankshaft and a wind-electric spindle. Unlike single-stage water quenching, oil quenching or quenching in aqueous polymer solution, ATQ avoids cracking of large workpieces during heat treatment and can produce high levels of mechanical properties. This n...

Research of economy alloyed of titanic alloy with the set chemical composition

The study of the structure and mechanical properties of sparingly alloyed sintered titanium alloy Ti0,25O1,5Fe, obtained by hydride powder metallurgy of titanium using spongy titanium as a raw material with a specified composition of alloying elements O and Fe, was conducted. The sintering of samples was conducted at the temperature of 1310 °C, based upon the results of our own research, as well as the sintering modes of industrial sintered titanium alloy 2М2А: heating in vacuum furnace with a speed of 20 °C/min to a temperature of 1310 °C and shutter speed of 4 hours. At the temperature 500 °C a shutter speed of 1 hour was carried out to prevent cracking of the material as a result of heavy hydrogen emission. Titanium sponge of fractions from 0 to 2 mm was treated with vibrating screening and sieving at the installation with the receipt of titanium sponge powder of fraction from 0,08 to 0,45 mm with a given content of oxygen and iron. The studied titanium sponge powder, compared with the requirements of the normative document, after its processing and allocation in separate fraction, contained alloying elements O and Fe at a level acceptable to the desired composition of alloying (O — 0,25 % (mass.), Fe — 1,5 % (mass.)), by the content of other impurities it corresponded to the highest grades of titanium sponge. Titanium sponge with a specified composition of alloying elements (O — 0,25 % (mass.), Fe — 1,5 % (mass.)) was obtained. On its basis sparingly alloyed sintered Ti alloy Ti0,25O1,5Fe was developed having a high level of mechanical properties: σВ — 630 MPa, δ — 7 % and ψ — 28 %. The conclusions were made about the economic attractiveness of use of titanium sponge with a given chemical composition as a raw material for the production of sparingly alloyed sintered titanium alloys.

Calculation-experimental study of the phase composition of Al-Zn-Mg-(Cu)-Ni-Fe aluminum alloys

To optimize the compositions of new high-strength aluminum ATs7NZh and ATs6N0.5Zh alloys (economically alloyed nikalins), the thermodynamic optimization of the Al-Zn-Mg-Cu-Ni-Fe system is performed via the construction of polythermal sections and the calculation of the chemical composition and volume fraction of phases at characteristic temperatures. The concentrations of the matrix elements (Zn, Mg, Cu) that determine the high level of mechanical properties are shown to be 6–7 wt % Zn, 2–3 wt % Mg, and up to 0.3 wt % Cu. The concentrations of the eutectic-forming elements (Ni, Fe) that ensure the solidification of (Al) + Al9FeNi eutectic are determined. This eutectic favors an increase in the manufacturing properties of the alloys during casting, metal forming, and welding along with a retained high level of the mechanical properties. In general, experimental results confirm the calculated data.

Microstructure and mechanical properties of disperse reinforced composite material with AZ91 matrix alloy

In this work, the microstructures and mechanical properties of cast composite materials based on AZ91 magnesium alloy reinforced with silicon carbide or titanium particles are considered. The sensibility of poly reinforcement of AZ91 alloy by these particles is discussed. It is assumed that introduction of a mixture of SiC and Ti powders in the melt will provide achievement of a higher level of mechanical properties owing to the difference in plasticity and interphase strength of various reinforcing materials and the matrix.

The Effect of Time and Temperature Variations during Isothermal Annealing on the Mechanical Properties of High Carbon Bainitic Steel

The industrial development require new materials characterized highest mechanical properties. The conditions of thermo-mechanical treatment proved to highest level of mechanical properties for steels. Another method of making strong materials is to reduce the scale of the microstructure using heat treatment [1]. The paper presents the results of investigation into the effect of time and temperature variations during isothermal annealing on the mechanical properties of high carbon (c.a. 0,8%C) bainitic steel. Chemical composition of that steel (addition Si, Mn, Mo and Cr) obtain high level of tensile strength and good plastic properties. The analyzing of published results of researches of high carbon bainitic steels shown, that transformation of bainite can take between 2 to 60 days within the temperature range 125÷325°C [2,3] Based on results of researches of investigated steel a isothermal annealing in temperature range 200÷300°C were done. The experiments were done for 24, 50 and 100 hours of annealing. After that the mechanical tests were done. A Zwick Z100 testing machine was used for tests. The force and elongation values were recorded. On their basis, the proof stress and tensile strength of the steel tested were determined as a function of annealing temperature. The microstructure were determinated too.

Novel use of biodegradable casein conduits for guided peripheral nerve regeneration

Recent advances in nerve repair technology have focused on finding more biocompatible, non-toxic materials to imitate natural peripheral nerve components. In this study, casein protein cross-linked with naturally occurring genipin (genipin-cross-linked casein (GCC)) was used for the first time to make a biodegradable conduit for peripheral nerve repair. The GCC conduit was dark blue in appearance with a concentric and round lumen. Water uptake, contact angle and mechanical tests indicated that the conduit had a high stability in water and did not collapse and cramped with a sufficiently high level of mechanical properties. Cytotoxic testing and terminal deoxynucleotidyl transferase dUTP nick-end labelling assay showed that the GCC was non-toxic and non-apoptotic, which could maintain the survival and outgrowth of Schwann cells. Non-invasive real-time nuclear factor-κB bioluminescence imaging accompanied by histochemical assessment showed that the GCC was highly biocompatible after subcutaneous implantation in transgenic mice. Effectiveness of the GCC conduit as a guidance channel was examined as it was used to repair a 10 mm gap in the rat sciatic nerve. Electrophysiology, labelling of calcitonin gene-related peptide in the lumbar spinal cord, and histology analysis all showed a rapid morphological and functional recovery for the disrupted nerves. Therefore, we conclude that the GCC can offer great nerve regeneration characteristics and can be a promising material for the successful repair of peripheral nerve defects.

Biodegradable Glutaraldehyde‐crosslinked Casein Conduit Promotes Regeneration after Peripheral Nerve Injury in Adult Rats

In this study, GCC protein was used for the first time to construct a biodegradable conduit for peripheral nerve repair. The GCC was highly stable with a sufficiently high level of mechanical properties and it was non-toxic and non-apoptotic which could maintain the survival and outgrowth of Schwann cells. Noninvasive bioluminescence imaging accompanied with histochemical assessment showed the GCC was highly biocompatible after subcutaneous implantation in transgenic mice. Electrophysiology, labeling of calcitonin gene-related peptide in the lumbar spinal cord and histology analysis also showed a rapid morphological and functional recovery for disrupted rat sciatic nerves repaired with the GCC conduits. Therefore, we conclude that the GCC can offer great nerve regeneration characteristics and can be a promising material for the successful repair of peripheral nerve defects.

Synthesis and properties of lignin-highly branched poly (ester-amine) polymeric systems

Abstract Combined characteristics of hydrogen bonded/cross-linked polymer networks based on lignin motifs have been developed. This new type of polymeric material was prepared from an industrial lignin and a highly branched poly(ester-amine) (HBPEA) obtained by melt polycondensation of 1,1,1-triethanolamine (TEA) and adipic acid (AA). The lignin-HBPEA polymers were shown to be insoluble in common organic solvents and were characterized by FTIR and NMR spectroscopies. Thermo-mechanical measurements showed that melt mixing HBPEA with 40% lignin results in a flexible and tough material ( T g ; 7.7 °C and E′ 3.5 GPa). The hydrogen bonding recognition was based on various hydroxyl groups in lignin and aliphatic ester groups from HBPEA. The extent of interactions could be controlled by varying the amount of lignin added. These networks were thermally reversible and have highly tunable mechanical properties that were controlled by the extent of interactions. High level of mechanical properties could be achieved through the addition of lignin-poly(ester-amine) covalent cross-links. This study shows that the poly(ester-amine) structure plays an important role in the thermo-mechanical properties. By varying the spacer length between lignin and tertiary amine unit, materials with various thermo-mechanical properties were also obtained from the same parent polymer backbone.

Characteristics and biocompatibility of a biodegradable genipin‐cross‐linked gelatin/β‐tricalcium phosphate reinforced nerve guide conduit

To modulate the mechanical properties of nerve guide conduit for surgical manipulation, this study develops a biodegradable composite containing genipin cross-linked gelatin annexed with β-tricalcium phosphate ceramic particles as a nerve guide material. The conduit was dark bluish and round with a rough and compact outer surface compared to the genipin cross-linked gelatin conduit (without β-tricalcium phosphate). Water uptake and swelling tests indicate that the conduit noticeably increases the stability in water, and the hydrated conduit does not collapse and stenose. The conduit has a sufficiently high level of mechanical properties to serve as a nerve guide. After subcutaneous implantation on the dorsal side of a rat, the degraded conduit only evokes a mild tissue response, and the formation of a very thin fibrous capsule surrounds the conduit. This paper assesses the effectiveness of the conduit as a guidance channel when we use it to repair a 10 mm gap in the rat's sciatic nerve. The experimental results show no gross inflammatory reactions of the peripheral nerve tissues at the implantation site in either group. In overall gross examination, the diameter of the intratubular and newly formed nerve fibers in the conduits exceeds that of the silicone tubes during the implantation period. The quantitative results indicate the superiority of the conduits over the silicone tubes. This study microscopically observes the nerve regeneration in the tissue section at the middle region of all implanted conduits. Therefore, the histomorphometric assessment demonstrates that the conduit could be a candidate for peripheral nerve repair.

Production of Nanostructure in Titanium by Cold Rolling

The paper considers changes in microstructure, texture and mechanical properties of commercial titanium with initial coarse-grained structure during cold sheet rolling. It has been shown that rolling above 75% leads to formation of a uniform nanocrystalline (NC) structure with a grain size of approximately 0.2 'm in the sheet material. The sheets have a high level of mechanical properties which is comparable with the properties of bulk specimens of titanium with NC structure produced by some other method of severe plastic deformation.

SYNTHESIS OF ALLOY Ti − 6Al − 4V WITH LOW RESIDUAL POROSITY BY A POWDER METALLURGY METHOD

The possibility of producing titanium alloy Ti ― 6Al ― 4V with minimal residual porosity from mixtures of elemental powders by the method of pressing and sintering without hot deformation during or after sintering was investigated. Various powder mixtures based on titanium and titanium hydride with alloying additions of either elemental powders having different particle sizes, or master alloys, were studied. It was shown that the synthesis of Ti ― 6Al ― 4V from mixtures of titanium hydride and master alloys is optimal with respect to the attainment of high relative density. In this case the sintered material has density up to 99%, homogeneous microstructure with relatively small (100-120 μm) β-phase grains, and a low concentration of impurities, in particular oxygen, which provide a high level of mechanical properties σ(ten = 970 MPa, δ = 6%).

Effect of compressive stresses on deformation and contact phenomena in pressed fibrous materials during sintering

A study is made of the processes that control deformation and contact phenomena in porous fibrous metallic materials. It was established that sintering of fibrous materials which are subjected to small compressive stresses in the pressing direction makes it possible to completely suppress the volumetric growth of specimens, which is seen during pressing and sintering. Due to the reestablishment of interparticle contacts, the resulting specimens have a significantly higher level of mechanical properties. For example, the ultimate tensile strength of the specimens is increased by a factor of 1.5–2 compared to control specimens of the same porosity.

Criteria of the Applicability of Various Powders of Silicon Nitride in the Hot-Pressing Technology for Fabricating High-Density and High-Strength Materials

The possibility of providing a high level of mechanical properties in ceramic materials is proved experimentally by using hot pressing of highly active powders of silicon nitride obtained by plasmachemical synthesis (PCS) and self-propagating high-temperature synthesis (SHS). The requirements placed on the powders of silicon nitride used for the production of high-density and high-strength materials widen substantially.

On structural features responsible for the mechanical properties of ceramics from zirconia partially stabilized with Y3+ and Mg2+ ions

It is shown that Y-PSZ ceramics mainly fracture by an intercrystalline mechanism and the grain size fluctuates from 0.2 to 0.8 μm, whereas Mg-PSZ ceramics mainly fracture by a transcrystalline mechanism and the grain size fluctuates from 30 to 80 μm. The high level of mechanical properties is provided by compressive stresses that appear in the transformation of the β′-phase into the a-phase. In the Y-PSZ ceramics the transformation concerns individual grains, and in the Mg-PSZ ceramics lenticular segregations of the β′-phase are positioned in the γ-phase. The transformation is induced by tensile stresses of the elastic field of a crack, i.e., can be classified as transformation toughening.

Mechanical properties of flame-retardant polypropylene compositions

The application of pentabromobenzyl acrylate monomer (PBB-MA) extrusion polymerized in ethylene-propylene-diene monomer (EPDM) terpolymer allows the production of flame-retardant polypropylene (PP) with very high impact and elongation at break and good resistance to thermal aging. The explanation of the high level of mechanical properties and of thermal aging resistance of PP/(EPDM/PBB-MA) is based on the hypothesis of EPDM/PBB-MA graft polymerization on EPDM double bonds, resulting in PP amor-phization and in specific morphology: better dispersion of flame retardant (FR) in PP and in EPDM and the formation of a honeycomb structure of EPDM/PBB-MA particles. Addition of either EPDM/PBB-MA or EPDM + PBB-PA to glass-fiber-reinforced polypropylene (GFR PP) makes feasible the combining of two modes of PP toughening: via glass fiber reinforcement and via EPDM-based particle dispersion in PP matrix.

Properties of Silicides and Silicide Composites Densified by Pressureless Reactive Sintering

The difficulties of casting high melting silicides and their poor sinterability limit structural and functional applications up to now. Furthermore mechanical properties of single phase silicides (MoSi 2 , TiSi 2 , Ti 5 Si 3 ,…) are insufficient at room temperature (fracture toughness) and above the brittle to ductile transition (BTDT) (creep). Approaches for advantages are concentrated on silicide composites using different hard phases (SiC, TiB 2 , ZrO 2 ,…), mixtures of silicides (e.g. (Mo, W)Si 2 ) and introduction of ductile metallic phases (e.g Nb) for strengthening the matrix. Our investigations on MoSi 2 -composites using the reactive sintering technique of activated powder mixtures proved a high level of mechanical properties. In particular we found for 4-point bending strength: 500 MPa (RT) and 700 MPa (1100°C); K IC (crack prolongation method): 5 MPam 1/2 (0 Vol.% SiC) and 8,4 MPam 1/2 (30 Vol.% SiC), creep rate: 10-5 (0% SiC) 10-6 (30Vol.% SiC). This data are at least as high as reported by other authors but in contrary to the state of art the preparation of complex parts should be possible. Furthermore it was shown that the materials show good corrosion resistance under flue gas atmosphere with high gas pressures and high gas speed.

Structure and properties of mechanically alloyed steel PK50N2M

The possibility of improving the properties of powder metallurgy nickel—molybdenum steel PK50N2M by dispersing and homogenizing the initial powders via grinding in a high-energy planetary mill, followed by single pressing and sintering, and subsequent quenching and tempering, was investigated. It was established that structural heredity provided small pore size, high homogeneity, a favorable defect density and distribution, an optimal phase composition in the heat-treated steel, and a transformation under load. These features permitted the attainment of a high level of mechanical properties, even at relatively high porosities.

AIN-Based Ceramics - an Alternative to Si<sub>3</sub>N<sub>4</sub> and SiC in High-Temperature Applications?

Aluminium nitride ceramics retain a high level of mechanical properties at temperatures above 1000°C and possess good oxidation resistance due to the formation of protective alumina-based scales. Although silicon-based ceramics dominate high-temperature engineering applications, new composites based on AIN can challenge the leading position of Si 3 N 4 and SiC ceramics. This paper presents a brief analysis of the oxidation behaviour of AlN-based materials using experimental results obtained in the framework of the INTAS project High Temperature Corrosion and Protection of Engineering Ceramics. Two major groups of AlN-based materials that can be considered for structural applications at high-temperatures are: 1. AlN-SiC solid solutions and multiphase composites which can form mullite scales with better protective properties compared to SiO 2 , particularly in combustion atmospheres. 2. AlN-boride (TiB 2 , ZrB 2 and other) composites which form self/healing oxide scales containing refractory aluminium borates. These compositions can be used as bulk ceramics or protective coatings for C/C composites or other materials with low oxidation resistance. Advantages and limitations of AlN-based composites are discussed.

General laws governing variation in properties of cast alloys of the Al-Zn-Mg system

Among existing high-strength corrosion-resistant aluminum alloys, those of the Al-Mn-Zn system are most promising. They have a different phase composition, depending on the content of magnesium and Zinc: α + β(Al3Mg2), α + β + T(Al2Mg3Zn3), α + T, α + T + η (MgZn2) and α + η The majority of industrial Al-Mg-Zn alloys correspond to the phase regions α + T and α + T + η with respect to composition. A high level of strength and satisfactory overall corrosion resistance are characteristic for these alloys. Al-Mg-Zn alloys may, however, tend to the most dangerous form of corrosion - stress-induced corrosion cracking. Using methods of experiment planning in the study, we investigated Al-Zn-Mg alloys of various compositions for the purpose of selecting alloy compositions with a high level of mechanical properties and stress-induced corrosion cracking.

Tendency to brittle failure in annealed 28Kh3SNMVFA-Sh sheet steel

1. A steel with finer grains and a more widely dispersed carbide phase that is uniformly distributed relative to the grains has the least tendency to brittle failure and satisfactory stampability during explosive forming. 2. An increased tendency to brittle failure and, as a result, failure in sheets during explosive forming is related to the inappropriate structure, which is coarse and nonuniformly distributed within the carbide phase ferritic matrix. Presumably, the formation of such a structure is the result of excessively lengthy sheet annealing at the producer's plant. 3. The structure of the original steel can be improved by applying heat treatment. In this situation, the resistance to crack propagation is improved by a factor of 3 to 8. After this improving heat treatment, the annealed 28Kh3SNMVFA-Sh steel has a relatively high level of mechanical properties.