Дисертації з теми "Multi principal element alloys"

Bulk metallic glasses and multi-principal element alloys represent relatively new classes of multi-component engineering materials designed for satisfying multiple functionalities simultaneously. Correlating the microstructure with mechanical behavior (at the microstructural length-scales) in these materials is key to understanding their performance. In this study, the structure evolution and nano-mechanical behavior of these two classes of materials was investigated with the objective of fundamental scientific understanding of their properties. The structure evolution, high temperature nano-mechanical behavior, and creep of two Zr-based alloys was studied: Zr41.2Ti13.8Cu12.5Ni10.0Be22 (Vitreloy1) and Zr52.5Ti5Cu17.9Ni14.6All0 (Vitreloy105). Devitrification was found to proceed via the formation of a metastable icosahedral phase with five-fold symmetry. The deformation mechanism changes from inhomogeneous or serrated flow to homogenous flow near 0.9Tg, where Tg is the glass transition temperature. The creep activation energy for Vitreloy1 and Vitreloy105 were 144 kJ/mol and 125 kJ/mol, respectively in the range of room temperature to 0.75Tg. The apparent activation energy increased drastically to 192 kJ/mol for Vitreloy1 and 215 kJ/mol for Vitreloy105 in the range of 0.9Tg to Tg, indicating a change in creep mechanism. Structure evolution in catalytic amorphous alloys, Pt57.5Cu14.7Ni5.3P22.5 and Pd43Cu27Ni10P20, was studied using 3D atom probe tomography and elemental segregation between different phases and the interface characteristics were identified. The structure evolution of three multi-principal element alloys were investigated namely CoCrNi, CoCrFeMnNi, and Al0.1CoCrFeNi. All three alloys formed a single-phase FCC structure in as-cast, cold worked and recrystallized state. No secondary phases precipitated after prolonged heat treatment or mechanical working. The multi-principal element alloys showed less strain gradient plasticity compared to pure metals like Ni during nano-indentation. This was attributed to the highly distorted lattice which resulted in lesser density of geometrically necessary dislocations (GNDs). Dislocation nucleation was studied by low load indentation along with the evaluation of activation volume and activation energy. This was done using a statistical approach of analyzing the "pop-in" load marking incipient plasticity. The strain rate sensitivity of nanocrystalline Al0.1CoCrFeNi alloy was determined by in situ compression of nano-pillars in a Pico-indenter. The nanocrystalline alloy demonstrated a yield strength of ~ 2.4 GPa, ten times greater than its coarse grained counterpart. The nanocrystalline alloy exhibited high strain rate sensitivity index of 0.043 and activation volume of 5b3 suggesting grain boundary dislocation nucleation.

High entropy alloys (HEA) are a relatively new group of alloys first introduced in 2004. They usually contain 5 to 6 different principle elements. Each of these elements comprise 5-35 at. % of the chemical composition of the alloy. There is a growing interest in the research community about the development of these alloys as well as their engineering applications. Some HEAs have interesting properties that have made them well suited for higher temperature applications, particularly refractory uses, while some have been shown to maintain their mechanical properties even at cryogenic temperatures. Initially, the HEA research was focused on developing alloys with equiatomic compositions as it was believed that the single phase HEA would only form at such composition ratios. However, further research have found multiple HEAs with non-equiatomic chemical compositions. A major question that needs to be answered at this point is how to identify these non-equiatomic single phase alloy systems. Unlike the conventional alloys, the HEAs do not have a base element as a solvent, which complicates the identification of new alloy systems via conventional development techniques. To find a potential HEA, alloy development techniques of both exploratory and computational natures are being conducted within the community. Even though multiple HEAs have been successfully identified and fabricated by these techniques, in most cases they require extensive experimental data and are relatively time consuming and expensive. This study proposes a thin film combinatorial approach as a more efficient experimental method in developing new HEA alloy systems. In order to study HEA systems with different crystal structures, nominal HEA compositions were selected, including: CoFeMnNiCu in order to achieve face centered cubic (FCC) HEA, OsRuWMoRe to obtain hexagonal closed packed (HCP) and VNbMoTaW in an attempt to form a body centered cubic (BCC) crystal structure. Thin film samples were fabricated by simultaneous magnetron sputtering of the elements onto silicon wafer substrates. The arrangement of the sputtering targets yielded a chemical composition gradient in the films which ultimately resulted in the formation of various phases. Some of these phases exhibited the desired single-phase HEA, albeit with non-equiatomic chemical compositions. Bulk samples of the identified HEA compositions were prepared by arc melting mixtures of the metals. Microstructure of both thin film samples and bulk samples were characterized via scanning electron microscopy (SEM), focused ion beam (FIB) and energy dispersive x-ray spectroscopy (EDX). The crystal structures of the samples were studied by X-ray diffraction (XRD) and electron backscattered diffraction (EBSD) technique. Applying nano-indentation technique, the mechanical properties of some of the samples were screened over the composition gradient as well. By applying this combinatorial thin film approach, single-phase FCC, HCP and BCC HEAs were detected and successfully produced in bulk form. Additionally, screening the properties of the compositionally gradient thin films, as well as their chemical composition and crystal structure, provided a thorough understanding of the phase space. This experimental approach proved to be more efficient in identifying new alloy systems than conventional exploratory development methods.

AlNiCo magnets are known for high-temperature stability and superior corrosion resistance and have been widely used for various applications. Reported magnetic energy density ((BH) max) for these magnets is around 10 MGOe. Theoretical calculations show that ((BH) max) of 20 MGOe is achievable which will be helpful in covering the gap between AlNiCo and Rare-Earth Elements (REE) based magnets. An extended family of AlNiCo alloys was studied in this dissertation that consists of eight elements, and hence it is important to determine composition-property relationship between each of the alloying elements and their influence on the bulk properties. In the present research, we proposed a novel approach to efficiently use a set of computational tools based on several concepts of artificial intelligence to address a complex problem of design and optimization of high temperature REE-free magnetic alloys. A multi-dimensional random number generation algorithm was used to generate the initial set of chemical concentrations. These alloys were then examined for phase equilibria and associated magnetic properties as a screening tool to form the initial set of alloy. These alloys were manufactured and tested for desired properties. These properties were fitted with a set of multi-dimensional response surfaces and the most accurate meta-models were chosen for prediction. These properties were simultaneously extremized by utilizing a set of multi-objective optimization algorithm. This provided a set of concentrations of each of the alloying elements for optimized properties. A few of the best predicted Pareto-optimal alloy compositions were then manufactured and tested to evaluate the predicted properties. These alloys were then added to the existing data set and used to improve the accuracy of meta-models. The multi-objective optimizer then used the new meta-models to find a new set of improved Pareto-optimized chemical concentrations. This design cycle was repeated twelve times in this work. Several of these Pareto-optimized alloys outperformed most of the candidate alloys on most of the objectives. Unsupervised learning methods such as Principal Component Analysis (PCA) and Heirarchical Cluster Analysis (HCA) were used to discover various patterns within the dataset. This proves the efficacy of the combined meta-modeling and experimental approach in design optimization of magnetic alloys.

Design space exploration (DSE) is used to improve and understand engineering designs. Such designs must meet objectives and structural requirements. Design improvement is non-trivial and requires new DSE methods. Turbomachinery manufacturers must continue to improve existing engines to keep up with global demand. Two challenges of turbomachinery DSE are: the time required to evaluate designs, and knowing which designs to evaluate. This research addressed these challenges by developing novel surrogate and principal component analysis (PCA) based DSE methods. Node and PCA-based surrogates were created to allow faster DSE of turbomachinery blades. The surrogates provided static stress estimation within 10% error. Surrogate error was related to the number of sampled finite element (FE) models used to train the surrogate and the variables used to change the designs. Surrogates were able to provide structural evaluations three to five orders of magnitude faster than FEA evaluations. The PCA-based surrogates were then used to create a PCA-based design workflow to help designers know which designs to evaluate. The workflow used either two-point correlation or stress and geometry coupling to relate the design variables to principal component (PC) scores. These scores were projections of the FE models onto the PCs obtained from PCA. Analysis showed that this workflow could be used in DSE to better explore and improve designs. The surrogate methods were then applied to vibratory stress. A computationally simplified analysis workflow was developed to allow for enough fluid and structural analyses to create a surrogate model. The simplified analysis workflow introduced 10% error but decreased the computational cost by 90%. The surrogate methods could not directly be applied to emulation of vibration due to the large spikes which occur near resonance. A novel, indirect emulation method was developed to better estimate vibratory responses Surrogates were used to estimate the inputs to calculate the vibratory responses. During DSE these estimations were used to calculate the vibratory responses. This method reduced the error between the surrogate and FEA from 85% to 17%. Lastly, a PCA-based multi-fidelity surrogate method was developed. This assumed the PCs of the high and low-fidelities were similar. The high-fidelity FE models had tens of thousands of nodes and the low-fidelity FE models had a few hundred nodes. The computational cost to create the surrogate was decreased by 75% for the same errors. For the same computational cost, the error was reduced by 50%. Together, the methods developed in this research were shown to decrease the cost of evaluating the structural responses of turbomachinery blade designs. They also provided a method to help the designer understand which designs to explore. This research paves the way for better, and more thoroughly understood turbomachinery blade designs.

L’objectif principal de cette thèse est de développer des techniques de modélisation et de simulation multi-échelles avancées et efficaces pour les matériaux architecturés et composites à base d’Alliages à Mémoire de Forme (AMF). À cette fin, un modèle générique 3D multi-échelles pour les AMF architecturés est implémenté dans ABAQUS, où un modèle thermodynamique, proposé par Chemisky et al. [1], est adopté pour décrire le comportement constitutif local de l’AMF, et la méthode des éléments finis multi-échelles (EF2) pour réaliser l’interaction en temps réel entre le niveau microscopique et le niveau macroscopique. L’instabilité élastique des fibres au niveau microscopique est également étudiée efficacement dans ce cadre en introduisant la Méthode Asymptotique Numérique (MAN) et la Technique des Coefficients de Fourier à Variation Lente (TCFVL). Pour améliorer l’efficacité du calcul de l’approche simultanée à plusieurs échelles, dans laquelle d’énormes problèmes microscopiques sont résolus en ligne pour mettre à jour les contraintes macroscopiques, des méthodes de calcul multi-échelles basées sur les données sont proposées pour les structures composites. En découplant les échelles corrélées dans le cadre FE2, les problèmes microscopiques sont résolus hors ligne, tandis que le coût du calcul macroscopique en ligne est considérablement réduit. De plus, en formulant le schéma data-driven en contrainte et déformation généralisées, le calcul par la technique Structural-Genome-Driven est développé pour les structures composites à parois minces
The main aim of this thesis is to develop advanced and efficient multiscale modeling and simulation techniques for Shape Memory Alloys (SMAs) composite and architected materials. Towards this end, a 3D generic multiscale model for architected SMAs is implemented in ABAQUS, where a thermodynamic model, proposed by Chemisky et al. [1], is adopted to describe the local constitutive behavior of the SMA, and the multiscale finite element method (FE2) to realize the real-time interaction between the microscopic and macroscopic levels. Microscopic fiber instability is also efficiently investigated in this framework by introducing the Asymptotic Numerical Method (ANM) and the Technique of Slowly Variable Fourier Coefficients (TSVFC). To improve the computational efficiency of the concurrent mulitscale approach, in which tremendous microscopic problems are solved online to update macroscopic stress, data-driven multiscale computing methods are proposed for composite structures. Decoupling the correlated scales in concurrent FE2 framework, microscopic problems are solved offline, while the online macroscopic computational cost is significantly reduced. Further, by formulating the data-driven scheme in generalized stress and strain, Structural-Genome-Driven computing is developed for thin-walled composite structures

AA6061 Al alloys modified with addition of Mn, Cr and Cu were homogenized at temperatures between 350 ºC and 550 ºC after casting. STEM experiments revealed that the formation of α-Al(MnFeCr)Si dispersoids during homogenization were strongly affected by various factors such as heating rate, concentration of Mn, low temperature pre-nucleation treatment and homogenization temperature. Through analysis of the STEM results using an image software Image-Pro, the size distributions and number densities of the dispersoids formed during different annealing treatments were quantitatively measured. It was revealed that increasing the heating rate or homogenization temperature led to a reduction of the number density and an increase in size of the dispersoids. The number density of dispersoids could be markedly increased through a low temperature pre-nucleation treatment. A higher Mn level resulted in the larger number density, equivalent size and length/width ratio of the dispersoids in the alloy. Upsetting tests on two of these Mn and Cr-containing AA6061 (Al-Mg-Si-Cu) Al alloys with distinctive Mn contents were carried out at a speed of 15 mm s-1 under upsetting temperature of 450 ºC after casting and subsequent homogenization heat treatment using a 300-Tone hydraulic press. STEM experiments revealed that the finely distributed α-Al(MnFeCr)Si dispersoids formed during homogenization showed a strong pinning effect on dislocations and grain boundaries, which could effectively inhibit recovery and recrystallization during hot deformation in the two alloys. The fractions of recrystallization after hot deformation and following solution heat treatment were measured in the two alloys with EBSD. It was found that the recrystallization fractions of the two alloys were less than 30%. This implied that the finely distributed α-dispersoids were rather stable against coarsening and they stabilized the microstructure by inhibiting recovery and recrystallization by pinning dislocations during deformation and annealing at elevated temperatures. By increasing the content of Mn, the effect of retardation on recrystallization were further enhanced due to the formation of higher number density of the dispersoids. STEM and 3-D atom probe tomography experiments revealed that α-Al(MnFeCr)Si dispersoids were formed upon dissolution of lathe-shaped Q-AlMgSiCu phase during homogenization of the modified AA6061 Al alloy. It was, for the first time, observed that Mn segregated at the Q-phase/matrix interfaces in Mn-rich regions in the early stage of homogenization, triggering the transformation of Q-phase into strings of Mn-rich dispersoids afterwards. Meanwhile, in Mn-depleted regions the Q-phase remained unchanged without segregation of Mn at the Q-phase/matrix interfaces. Upon completion of α-phase transformation, the atomic ratio of Mn and Si was found to be 1:1 in the α-phase. The strengthening mechanisms in the alloy were also quantitatively interpreted, based on the measurements of chemical compositions, dispersoids density and size, alloy hardness and resistivity as a function of the annealing temperature. This study clarified the previous confusion about the formation mechanism of α-dispersoids in 6xxx series Al alloys. Four-point bend fatigue tests on two modified AA6061 Al alloys with different Si contents (0.80 and 1.24 wt%, respectively) were carried out at room temperature, f = 20 Hz, R = 0.1, and in ambient air. The stress-number of cycles to failure (S-N) curves of the two alloys were characterized. The alloys were solution heat treated, quenched in water, and peak aged. Optical microscopy and scanning electron microscopy were employed to capture a detailed view of the fatigue crack initiation behaviors of the alloys. Fatigue limits of the two alloys with the Si contents of 0.80 and 1.24 wt% were measured to be approximately 224 and 283.5 MPa, respectively. The number of cracks found on surface was very small (1~3) and barely increased with the applied stress, when the applied stress was below the yield strength. However, it was increased sharply with increase of the applied stress to approximately the ultimate tensile strength. Fatigue crack initiation was predominantly associated with the micro-pores in the alloys. SEM examination of the fracture surfaces of the fatigued samples showed that the crack initiation pores were always aspheric in shape with the larger dimension in depth from the sample surface. These tunnel-shaped pores might be formed along grain boundaries during solidification or due to overheating of the Si-containing particles during homogenization. A quantitative model, which took into account the 3-D effects of pores on the local stress/strain fields in surface, was applied to quantification of the fatigue crack population in a modified AA6061 Al alloy under cyclic loading. The pores used in the model were spherical in shape, for simplicity, with the same size of 7 μm in diameter. The total volume fraction of the pores in the model were same as the area fraction of the pores measured experimentally in the alloy. The stress and strain fields around each pore near the randomly selected surface in a reconstructed digital pore structure of the alloy were quantified as a function of pore position in depth from the surface using a 3-D finite element model under different stress levels. A micro-scale Manson-Coffin equation was used to estimate the fatigue crack incubation life at each of the pores in the surface and subsurface. The population of fatigue cracks initiated at an applied cyclic loading could be subsequently quantified. The simulated results were consistent with those experimentally measured, when the applied maximum cyclic stress was below the yield strength, but the model could not capture the sudden increase in crack population at UTS, as observed in the alloy. This discrepancy in crack population was likely to be due to the use of the spherical pores in the model, as these simplified pores could not show the effects of pore shape and their orientations on crack initiation at the pores near surface. Although it is presently very time-consuming to calculate the crack population as a function of pore size and shape in the alloy with the current model, it would still be desirable to incorporate the effects of shape and orientation of the tunnel-shaped pores into the model, in the future, in order to simulate the fatigue crack initiation more accurately in the alloy.

Les excellentes proprietes mecaniques des superalliages leurs sont conferees par la precipitation de la phase gamma prime issue des divers traitements thermiques. L'etape de trempe qui succede a l'elaboration par metallurgie des poudres des disques de turboreacteur en superalliage a base de nickel, conditionne fortement l'etat mecanique et microstructural final du materiau. L'objectif de ce travail est de developper et de valider un modele qui decrit la cinetique de precipitation de la phase gamma prime afin d'optimiser la microstructure resultant de cette trempe. Une serie de demarches experimentales a permis d'analyser et d'identifier le comportement du materiau au cours de ce traitement thermique. L'influence de la vitesse de refroidissement sur la microstructure finale et sur l'allure de la fraction volumique transformee est etudiee experimentalement par dilatometrie de trempe et observation electronique a transmission. Ces observations montrent que la coalescence s'effectue suivant la loi de lsw et que l'on retrouve la sequence de transformation morphologique sphere cube octocube dendrite observee dans le cas des transformations anisothermes. La dilatometrie permet egalement de mettre en evidence le domaine de precipitation de la phase gamma prime. De la meme facon, l'influence de la temperature de mise en solution sur la microstructure et sur la fraction volumique f#v est analysee. De plus, les enregistrements dilatometriques permettent d'apprecier la dissolution de la phase gamma prime en cours de chauffage a partir de microstructures variees. Enfin, la microstructure du n18 en cours de refroidissement est suivie par hyper-trempe a environ 10#5 k/s dans un four concu specialement pour cette etude. Une famille tres fine de phase gamma prime est mise en evidence par met et diffusion de neutrons aux petits angles. L'ensemble des resultats obtenus permettent de valider le modele base sur la theorie classique de nucleation et les lois de coalescence de lsw et permet de rendre compte de la capacite du calcul a decrire la precipitation intragranulaire (secondaire et tertiaire) au cours de traitements thermiques divers

Les Alliages à Mémoire de Forme Magnétiques (AMFM) sont des matériaux actifs qui présentent des comportements inhabituels par rapport aux matériaux " classiques ". Ils peuvent par exemple présenter de larges déformations réversibles sous l'action d'un champ magnétique ou sous une action mécanique. Ce sont des candidats potentiels pour des applications dans des domaines de pointe (automobile, aéronautique, spatial, etc.). Les AMFM présentent par ailleurs un avantage indéniable par rapport aux matériaux à mémoire de forme " thermique " en raison de leur réponse dynamique à haute fréquence. Il est bien connu que ces comportements sont dus à un couplage magnéto-mécanique et à un phénomène physique lié à l'orientation des variantes de martensite. L'objectif de cette thèse est d'analyser les comportements magnéto-mécaniques des AMFM. Pour ce faire, nous étudions expérimentalement et théoriquement, la réorientation martensitique dans les AMFM. Tout d'abord, une analyse énergétique en 2D/3D est proposée et intégrée dans des diagrammes d'état pour une étude systématique de la réorientation martensitique dans les AMFM sous chargements tridimensionnels quelconques. Ainsi, des critères de large déformation réversible sous des chargements cycliques sont obtenus. L'analyse énergétique montre que les AMFM, sollicités sous chargement multiaxiaux présentent plus d'avantages que ceux sollicités en 1D ; en particulier, on montre que l'état multiaxial permet d'augmenter (d'améliorer) la contrainte fonctionnelle, ce qui augmente le champ d'application des ces matériaux. Ensuite, afin de valider les prédictions de l'analyse énergétique, des expériences bi-axiales ont été effectuées sur des éprouvettes en AMFM. Les résultats révèlent que la dissipation intrinsèque et la déformation de transformation dues à la réorientation martensitique sont constantes dans tous les états de contraintes. De plus, les résultats ont permis de valider nos prédictions théoriques quant à l'augmentation de la contrainte fonctionnelle. Enfin, afin de prédire les comportements magnéto-mécaniques des AMFM sous des chargements multiaxiaux, un modèle tridimensionnel est développé dans le cadre de la thermodynamique des processus irréversibles avec liaison interne. Toutes les variantes de martensite ont été considérées et l'effet de température a également été pris en compte. Les simulations numériques montrent un très bon accord (rejoignent/confirment les résultats) avec les résultats expérimentaux existant dans la littérature. Le modèle a ensuite été programmé dans un code de calcul par éléments finis afin d'étudier les comportements non linéaires de flexion des poutres en AMFM. L'effet géométrique et l'effet d'anisotropie du matériau ont été systématiquement pris en compte.

碩士
國立清華大學
材料科學工程學系
102
This study investigates the superconductivity of as-cast and as-heat-treated ternary to 6-element multi-component alloys (hereafter abbreviated as the alloys) that are made of non-equal molar Nb-Zr-Ti by addition of minor Hf, V, Ta and Ge. The alloys are principally single random BCC Nb-rich solid solutions. Difference in formation enthalpies between elements, especially for pairs with Ta and Ge, and the driving forces by heat treatments induce a Zr-bearing precipitation from the Nb-rich BCC phase to form a Zr(Ge)-rich phase. This results in a change of Nb/Zr ratio in the Nb-rich BCC phase, and thus affects the superconductivity of the alloys. The critical temperature of the alloys, Tc, ranges from 8 K to 11 K. The room-temperature resistivity of the as-cast alloys varies from 21 μΩ–cm to 35 μΩ–cm. Compared with the electrical resistivity of other multi-component ones, the alloys have a lower electrical resistivity. The residual resistivity ratio RRR value is from 1.2 to 1.3, which mentions that the resistivity is principally controlled by the impurity atoms in the alloys. If one simply emphasizes the e/a ratio from the content of Nb and Zr in the alloys, the Tc of the alloys approximately follows the Matthias empirical rule. However, factors affecting Tc, besides the e/a, include lattice distortion due to multiple element addition, and the characteristics of individual elements in the alloys. The alloys are typically type II superconductors. The upper critical magnetic field Hc2 is estimated to be in the range of 5 T to 9 T. At 2 K &; 5 T, the critical current density Jc has the value of approximately 105 A/cm2. This property has something to do with the precipitates and has yet nothing to do with the lattice distortion of the alloys.

碩士
國立清華大學
材料科學工程學系
92
A good thermoelectric material requires high Seebeck coefficient (S) and electrical conductivity (σ) but low thermal conductivity (κ), which are not common found in traditional metallic alloys. As compound with traditional metallic alloy, high entropy alloy of multi constituent element is a newly developed metallurgical concept. A variety of different forms of the multi-element alloys have been demonstrated to possess superior mechanical and chemical properties. However, the electrical and thermoelectric properties of the multi-element alloys have not been thoroughly explored yet. In this study, multi-element alloys were prepared by arc-melting and thermal annealing. Their thermoelectric properties were characterized after appropriate sample preparation. We find two multi-element alloy systems based on half-Heusler structure：ZrTiSnSiNi2 and ZrTiSnGeNi2. The thermoelectric figure of merits (ZT , Z= S2/(ρ×κ)) of these multi-element alloys were equal to be 0.02 and 0.045, respectively, at room temperature. These multi-element alloys showed 3 times increase in power factor (S2/ρ) in the middle temperature range (250℃ to 300℃). By adding Nb element into the alloy forming Zr0.9Ti0.9Nb0.2SnSiNi2, the thermoelectric figure of merit was found to be 0.078 at room temperature. The multi- element alloys were identified to be a composite material containing semiconductor-like phase and metallic-like phase by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS).

碩士
國立清華大學
材料科學工程學系
94
A effect of Sb doping (x=0~0.5) on the thermoelectric properties of annealed Ti0.5Zr0.5NiSn1-xSbx multi-element alloys is studied based on Ti0.5Zr0.5NiSn quaternary alloy with half-Heusler structure. The result shows both the absolute value of Seebeck coefficient and electrical resistivity decrease as the quantity of Sb doping increases at room temperature. The change of resistivity is marked for the alloy with slight Sb doping. The maximum power factor(S2/λ) is 2.83×10-3W/m-K2 for the annealed Ti0.5Zr0.5NiSn1-xSbx (x=0.005) alloy. It is three times larger than that of Ti0.5Zr0.5NiSn which is 0.72×10-3W/m-K2. The maximum ZT value is about 0.16 for the Ti0.5Zr0.5NiSn1-xSbx (x=0.005) alloy at room temperature which is four times larger than that of Ti0.5Zr0.5NiSn. Therefore, the lightly Sb doping would dramatically improve the thermoelectric properties of the Ti0.5Zr0.5NiSn alloy system. Besides, the results of thermoelectric properties measurement at high temperature reveal that the absolute value of Seebeck coefficient increases as the temperature rises. The resistivity of Sb doped alloys increases with rising temperature, indicating that the Sb doping would promote the metallic transport properties. Consequently, a slight Sb doping (below 5at% substitution of Sn atoms)would enhance the thermoelectric properties of Ti0.5Zr0.5NiSn1-xSbx alloy system.