Effects of second phases on mechanical properties and martensitic transformations of ECAPed TiNi and Ti-Mo based shape memory alloys

TiNi and Ti-based shape memory alloys were processed by equal channel angular pressing （ECAP） at 673-773 K along Bc route to obtain ultrafine grains for increasing the strength of parent phase and improving the functional properties. The effects of both thermodynamically stable and metastable second phases on the mechanical properties and martensitic transformations of these alloys were investigated. It is found that thermodynamically stable Ti2Ni phase has no effect on martensitic transformation and superelasticity of Ti-rich TiNi alloy, thermodynamically stable α phase is harmful for ductility of Ti-Mo-Nb-V-Al alloy, but metastable Ti3Ni4 phase is effective for R phase transformation, martensitic transformation and superelasticity of Ni-rich TiNi alloy. The mechanisms of the second phases on the martensitic transformations and mechanical properties were discussed.

Microstructure and mechanical properties of Al_3Ti-based alloys in Al-Ti-Mo-X quaternary systems

A part of Al-Ti-Mo-Cr quaternary phase diagram is constructed for themicrostructure control of D0_(22)-Al_3Ti or its derivative, L1_2-(Al,Cr)_3Ti, -based alloys. It wasfound that quaternary bcc phase equilibrates with either D0_(22)-Al_3Ti or L1_2-(Al,Cr)_3Ti, orboth, exist in large compositional areas. The mechanical properties is strongly affected byprecipitates appearing, and presumably alloy microstructures.

Effects of V and Zr Additions on Microstructures and Mechanical Properties of Nb-Ti-Al-Base Alloys

Microstructures and mechanical properties of Nb-32Ti-7Al alloys containing different V and Zr contents were investigated. The microstructures were characterized using optical microscopy and scanning electron microscopy (SEM). The alloy with V and Zr presents single phase Nb solid solution (Nbss). Tensile testing was carried out at room temperature and 1373 K. The results show that these alloys have good ductility at room temperature. The strengths at room and high temperature increase with the addition of V and Zr, but the room temperature ductility decrease.

Formation and mechanical properties of ductile Fe-based amorphous alloys using a cast iron with minor addition of B and Al

Fe-based amorphous alloys with ductility were synthesized using the commercial cast iron QT50 (denoted as QT) with the combining minor addition of B and Al by single roller melt-spinning. The melt-spun (QT1-xBx)99Al1 (x is from 0.006wt% to 0.01wt%) amorphous alloys exhibit onset crystallization temperatures and Curie temperatures of 759-780 and 629-642 K respectively, and whi- ch increase with B content. The amorphous ribbons are ductile and can be bent 180° without breaking. With the increase in B content from 0.006wt% to 0.01wt%, the Vickers microhardness of the amorphous alloys increases from Hv 830 to Hv 1110. The effects of the additional B and Al elements on the glass forming ability and mechanical properties were also discussed.

Effect of Si content on mechanical properties of Nb-Si based alloys with Nb_(ss)/ Nb_5Si_3 structure

In Nb-Si based alloys with a two-phase Nbss/ intermetallic Nb5Si3 structure, the Nb5Si3 provides high-temperature strength, while the Nb solid-solution phase, Nbss, contributes to room-temperature ductility and toughness. The results show that in Nb-15W-10Hf-xSi alloys (x= 0.5, 5 and 18, mole fraction, %), the volume fraction of the Nb5Si3 is 0 for the 0.5% Si sample, 15% for the 5% Si sample and the 50% for 18% Si sample. With increasing Si content, i.e., the Nb5Si3 fraction, the high-temperature strength is improved considerably, but room-temperature ductility and toughness are degraded. For the sample Nb-15W-10Hf-18Si with 50% Nb5Si3, the compressive strength at 1 500℃and the room-temperature fracture toughness are 500 MPa and 6.8 MPa·m1/2, respectively, those for the Nb5Si3 free sample, Nb-15W-10Hf-0.5Si, are 190 MPa and 13.6 MPa·m1/2.

Formation and Mechanical Properties of Zr-Nb-Cu-Ni-Al-Lu Bulk Glassy Alloys with Superior Glass-Forming Ability

Glass-forming ability（GFA） and mechanical properties of（Zr_（0.58）Nb_（0.03）Cu_（0.16）Ni_（0.13）Al_（0.10））_（100-x）Lu_x（x= 0-3 at%） alloys have been investigated.The GFA of Zr_（58）Nb_3Cu_（16）Ni_（13）Al_（10） alloy is dramatically enhanced by adding Lu.The（Zr_（0.58）Nb_（0.03）Cu_（0.16）Ni_（0.13）Al_（0.10））_（98）Lu_2 alloy possesses the highest GFA in the studied Zr-Nb-Cu-Ni-Al-Lu alloys,with its critical diameter for glass formation reaching 20 mm by copper-mould casting method,while that of the Lu-free Zr_（58）Nb_3Cu_（16）Ni_（13）Al_（10） alloy is 7 mm.The critical diameters of（Zr_（0.58）Nb_（0.03）Cu_（0.16）Ni_（0.13）Al_（0.10））_（100-x）Lu_x（x =1 at%and 3 at%） alloys are 15 mm and 12 mm,respectively.The Lu addition to Zr_（58）Nb_3Cu_（16）Ni_（13）Al_（10） alloy induces the change of initial crystallization phases from face-centred-cubic Zr_2Ni and tetragonal Zr_2Ni phases for the Lu-free Zr_（58）Nb_3Cu_（16）Ni_（13）Al_（10） alloy to an icosahedral quasi-crystalline phase for the Lu-doped alloys,which may be the origin for the enhanced GFA of the Lu-doped alloys.The compressive fracture strength and plastic strain of the bulk glassy（Zr_（0.58）Nb_（0.03）Cu_（0.16）Ni_（0.13）Al_（0.10））_（98）Lu_2 alloy are1 610 MPa and 1.5%,respectively.

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF TiAl+Nd ALLOYS

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Design and preparation of Zn-based materials possessing both high damping and good mechanical properties

A new idea of design and manufacture of metal based materials possessing both high damping and good mechanical properties was proposed. The key of the idea is the combination of fining restriction damping structures, using all mechanisms and taking advantages of different materials. Based upon this idea a foam ZA27 was prepared by the technology of prefabricated salt mass centrifugal seeping foundry, its tensile strength and compressive strength are 83～119?MPa and 100～189?MPa, respectively. The damping properties of the foam ZA27 increase remarkably after the carpenter pastern or rosin (the damping increased materials) was immerged into it, which approaches to the level of viscous elastic polymer materials ( Q -1 ≥20×10 -3 ). [

Effect of vacuum degree in VIM furnace on mechanical properties of Ni-Fe-Cr based alloy

In order to investigate the effect of the vacuum degree in vacuum induction melting （VIM） furnace on the mechanical properties of Ni-Fe-Cr based alloy, four samples were prepared under different conditions. The chemical analysis results show that under the argon atmosphere, there is more dissipation in Al and Ti, whereas it is reduced by establishing the vacuum atmosphere. The gas analysis results show that the oxygen and nitrogen contents of the samples decrease with increasing vacuum degree. However, there is no dissipation in the gas content of the samples in higher degree of vacuum. In addition, the thermodynamic calculations show that the probability of TiO2 and Al2O3 formation is high due to the small value of the equilibrium oxygen. Higher vacuum degree reduces the tensile and yield strength of the alloys, while it enhances the elongation and reduction of area values due to the lower amount of the inclusions and evaporation of Al and Ti under higher vacuum. On the other hand, increasing vacuum degree changes the fracture mode from brittle to ductile.

Microstructure and room temperature mechanical properties of NiAl-Cr(Mo)-(Hf,Dy) hypoeutectic alloy prepared by injection casting

The NiA1 Cr（Mo） （Hf, Dy） hypoeutectic alloys were prepared by conventional casting and injection casting techniques respectively, and their microstructure and room temperature mechanical properties were investigated. The results reveal that with the addition of Hf and Dy, the Ni2AIHf Heusler phase and NisDy phase form along the NiAI/Cr（Mo） phase boundaries in intercellular region. By the injection casting method, some Ni2AIHf Heusler phase and NisDy phase transform into Hf and Dy solid solutions, respectively. Moreover, the microstructure of the alloy gets good optimization, which can be characterized by the fine interlamellar spacing, high proportion of eutectic cell area and homogeneously distributed fine Ni2AIHf, NisDy, Hf solid solution and Dy solid solutions. Compared with conventional-cast alloy, the room temperature mechanical properties of injection-cast alloy are improved obviously.

Effects of induction heat treatment on mechanical properties of TiAl-based alloy

The effects of rapid heating cyclic heat treatment on mechanical properties of a TiAl based alloy (Ti 33Al 3Cr) were studied by means of an induction heating machine. The results show that: 1) fine fully lamellar microstructure with colony size of about 50 μm and lamellar spacing of about 0.12 μm can be obtained; 2) the compression mechanical properties can be improved to a large extent and the best comprehensive compression mechanical properties can reach the yield stress 745 MPa, the large flow stress 1 672 MPa and the compression ratio 19.4%; and 3) the compression fracture at room temperature after induction heat treatment and aging is still typical cleavage fracture.

Mechanical properties and tribological behavior of a cast heat-resisting copper based alloy

Mechanical properties and tribological behavior of a novel cast heat resisting copper based alloy are investigated. The corresponding properties of a commercial aluminum bronze C95500 (ASTM B30) are compared with the alloy. The results show that the alloy possesses better mechanical properties and tribological behaviors than that of C95500 at elevated temperature. The tensile strength, elongation and hardness at 500℃ are 470MPa, 2.5% and HB220, respectively. The wear rate of the developed alloy at ambient and elevated temperature is about one sixth and one fortieth of that of C95500, respectively. The alloy is very suitable for ma nufacturing heat resisting and wear resisting parts. Major strengthening mechanisms for the alloy are solution strengthening and the second phase strengthening.

Effect of pressure on microstructures and mechanical properties of Al-Cu-based alloy prepared by squeeze casting

A new high-strength aluminum alloy with better fluidity than that of ZL205A was developed. The effect of applied pressure during squeeze casting on microstructures and properties of the alloy was studied. The results show that the fluidity of the alloy is 16% and 21% higher than that of ZL205A at the pouring temperature of 993 K and 1 013 K, respectively. Compared with permanent-mold casting, mechanical properties of the alloy prepared by squeeze casting are much higher. The tensile strength and elongation of the alloy are 520 MPa and 7.9% in squeeze casting under an applied pressure of 75 MPa, followed by solution treatment at 763 K for 1 h and at 773 K for 8 h, quenching in water at normal temperature and aging at 463 K for 5 h. The improvement of mechanical properties is attributed to the remarkable decreasing of the secondary dendrite arm spacing(SDAS) and eliminating of micro-porosity in the alloy caused by applied pressure.

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF A Ni_3Al-Fe BASED ALLOY

The microstructure,tensile properties at 20—950℃ and creep rupture properties at 700- 900℃ in a Ni_3Al-Fe based alloy after high temperature deformation have been studied.The results show the microstructure of the alloy is composed of γ′-and β-phases.The grain size and yield strength of the alloy is stable when the temperature≤600℃,and it is ductile at high temperature.The creep of the alloy at 700—900℃ is controlled by the climbing of dislo- cations,and the activation energy for creep is 439 KJ/mol with a stress exponent of 4.

Mechanical properties of Mg-Gd-Zr alloy by Nd addition combined with hot extrusion

The effect of Nd addition on the microstructure and mechanical properties of as-extruded Mg-9Gd-0.5Zr(wt.%) alloy was investigated. The Mg-9Gd-0.5Zr and Mg-9Gd-2Nd-0.5Zr alloys were extruded at 673 K. The elongated non-dynamic recrystallized(un-DRXed) grains disappear after adding Nd, and uniformly distributed dynamic recrystallized grains with a grain size of 1.68 μm were obtained in the alloy. In addition, numerous nano-Mg5(Gd,Nd)particles were found to precipitate dynamically in the Mg-9Gd-2Nd-0.5Zr alloy, which gave rise to the dynamic recrystallization process via providing nucleation energy through hindering the release of deformation energy and promoting an increase in the strength through the Orowan strengthening mechanism. Moreover, the dynamically recrystallized(DRXed) grains have a weak texture, which plays a significant role in improving the ductility. Therefore,the Nd addition favors the improvement of strength and elongation for the as-extruded Mg-9Gd-0.5Zr alloy,simultaneously.

Effect of Pr addition on microstructure and mechanical properties of AZ61 magnesium alloy

To improve the strength, hardness and heat resistance of Mg-6Al-lZn （AZ61） alloy, the effects of Pr addition on the as-cast microstructure and mechanical properties of AZ61 alloy were investigated at room and elevated temperatures by means of Brinell hardness measurement, optical microscope （OM）, scanning electron microscope （SEM）, energy dispersive spectroscopy （EDS）, X-ray diffractometer （XRD） and DNS100 electronic universal testing machine. The results show that the microstructures of Pr-containing AZ61 alloys were refined, with primary,β-MglTAI12 phase distributed homogeneously. When the addition of Pr is up to 1.2wt.%, theβ phase becomes finer, and new needle-like or short-rod shaped AI11Pr3 phase and blocky AIPr phase appear. As a result, optimal tensile properties are obtained. However, greater than 1.2wt.% Pr addition leads to poorer mechanical properties due to the aggregation of the needle-like phase and large size of grains. The present research findings provide a new way for strengthening of magnesium alloys at room and elevated temperatures, and a method of producing thermally-stable AZ61 magnesium alloy.

Crystallization Behaviour and Mechanical Properties of Zr_(65)Cu_(18)Ni_9Al_8 Bulk Metallic Glass

Designing and synthesis of cost effective bulk metallic glasses （BMGs） has been of considerable interest during the last decade so that they can be made commercially viable. Among these, Zr-based BMGs have been reported extensively due to their attractive properties, An alloy having composition Zr65Cu18Ni9A18 was designed and synthesized using 2-3 N pure materials by Cu mould casting. The alloy was characterized by X- ray diffraction （XRD）, scanning electron microscopy （SEM）, energy dispersive X-ray spectroscopy （EDS） and high temperature differential scanning calorimetry （DSC）. Thermal parameters like supercooled liquid region △Tx, reduced glass transition temperature Trg, γ and δ parameters were evaluated. Mechanical properties like microhardness, nanohardness, elastic modulus and fracture strength were measured. The alloy showed wide supercooled liquid region of 129＋1 K with improved thermal stability. The alloy has considerable fracture strength along with fair amount of ductility.

Effects of Ta addition on the microstructure and mechanical properties of Ti_(40)Zr_(25)Ni_8Cu_9Be_(18) amorphous alloy

The effects of Ta addition on the microstructure and mechanical properties of Ti40Zr25Ni8Cu9Be18 bulk amorphous alloy were investigated by using X-ray diffraction (XRD), transmission electron microscopy (TEM), scan electron microscopy (SEM) and compressive testing. As a result, the addition of Ta (0-8at%) prompted the successive precipitation of quasicrystalline phase, CuTi2 phase and bcc β-Ti solid solution. Additionally, the addition of less Ta content (3at%-5at%) led to the formation of amorphous ma- trix/nanoquasicrystal/CuTi2 complex phase structure; and nanoquasicrystals, as reinforcement precipitates, improved the fracture strength of Ti-Zr-Ni-Cu-Be-Ta alloys, which led to the high compressive fracture strength 1856 MPa of Ta5 alloy. With increasing Ta content (5at%-8at%), although the ductile dendritic β-Ti solid solution was precipitated, the strength and plasticity decreased to a great extent resulting from the growth of quasicrystalline phase and CuTi2 phase.

STUDY ON ELEVATED TEMPERA-TURE MECHANICAL PROPERTIES OF AM50HP WITH ND

Effects of Nd on the mechanical properties of die casting magnesium alloysAM50 are investigated. It is found that the ultimate tensile strength, yield strength and elongationof the AM50 alloy at elevated temperatures up to 200 deg C increase with an addition of Nd.Generally, the most significant improvement in the tensile properties is attained at 100 deg C. Thepresence of Mg12Nd is proved by X-ray diffraction. Microstructural observations reveal that theaddition of Nd can lead to the dispersion-strengthening. Due to the presence of Mg12Nd, the slidingof grain boundaries is restrained and the strength of the alloy is enhanced. It can be seen from thetensile fractographs that the fracture surfaces exhibit the mixed fracture characteristics, andless brittle fracture is observed with increasing the temperature. Quasi-cleavage fracture isthought as the main fracture mode. TEM observations expose the formation of dislocation network,slip lines and dislocation pile-ups.