Lorsqu'une structure est soumise à un chargement thermique hétérogène, des dilatations empêchées génératrices de contraintes surviennent. Lorsque ces sollicitations sont répétées un grand nombre de fois, un endommagement puis une fissuration du matériau peuvent apparaître. On parle alors de fatigue thermique du matériau. Ce phénomène, jugé responsable de différents incidents rencontrés dans les zones de mélange entre fluides chaud et froid des centrales nucléaires a fait l'objet de nombreuses études lancées au sein de projets successifs pilotés par EDF. Ces études portaient sur la détermination des chargements thermo-hydrauliques dans les zones de mélange, le transfert de chaleur à la structure, la résolution du problème thermomécanique permettant de connaître les champs de contrainte et de déformation en tout point de la structure et enfin la résistance du matériau (un acier inoxydable austénitique AISI 304L)soumis à de telles sollicitations. Concernant ce dernier aspect, plusieurs types d'essais ont été réalisés : d'une part, des essais de fatigue uniaxiaux et isothermes pour construire une courbe de fatigue mécanique du matériau et, d'autre part, des essais sur plusieurs dispositifs expérimentaux de fatigue thermique développés au sein d'organismes de recherche (CEA, EDF, JRC, JAEA,…) pour s'approcher des conditions de service. L'interprétation de ces derniers essais passe par l'estimation des champs de température et de déplacement dans la structure à partir de quelques mesures ponctuelles de température par thermocouples. On constate alors que les premières fissures s'amorcent en fatigue thermique pour un nombre de cycles sensiblement inférieur à celui estimé à partir des courbes de fatigue mécanique du matériau et de l'amplitude maximale de déformation équivalente estimée dans les essais de fatigue thermique. L'objet de ce travail de thèse consiste donc à concevoir et à réaliser des chocs thermiques sur un matériau de structure couplés à des mesures synchrones et sans contact de champs de température et de déplacement au niveau de la surface endommagée. Les chocs thermiques seront réalisés à l'aide d'un laser de puissance dont la longueur d'onde sort du spectre utilisé par la caméra infrarouge qui mesure le champ de température de surface de telle manière que le dépôt d'énergie n'affecte pas les mesures de température. Plusieurs pistes sont envisagées selon que les champs sont mesurés uniquement avec la caméra infrarouge ou en utilisant deux caméras, l'une travaillant dans l'infrarouge et l'autre dans le visible. Dans les deux cas de figure, l'absorptivité et l'émissivité de la surface soumise au choc thermique doivent être optimisées pour permettre d'avoir à la fois un dépôt d'énergie homogène par laser et une mesure précise des champs thermomécaniques. Une difficulté qu'il conviendra de surmonter est d'obtenir un champ d'émissivité de surface représentant un compromis acceptable entre une émissivité forte et homogène dans l'infrarouge pour des mesures de température et une émissivité hétérogène (dans l'infrarouge ou le visible selon la caméra utilisée) pour créer un contraste de niveau de gris indispensable aux mesures de déplacement par corrélation d'images. Parallèlement aux essais,des simulations numériques thermomécaniques seront également réalisées pour compléter ces champs en volume et tester l'influence des conditions aux limites. L'objectif final de la thèse est d'obtenir pour la première fois une mesure fiable des quantités d'intérêt dans une zone d'amorçage en fatigue thermique et ainsi pouvoir quantifier convenablement un éventuel effet aggravant des sollicitations de fatigue thermique. / Thermal fatigue occurs in nuclear power plant pipes. The temperature variations are due to the turbulent mixing of fluids that have different temperatures. Many experimental setups have been designed but the measured temperatures have only been punctual and out of the zone of interest (e.g., via thermocouples). The equivalent strain variation in the crack initiation region is calculated with numerical thermomechanical simulations. In many cases, the comparisons between numerical and experimental results have shown that the crack initiation predictions in thermal fatigue are non-conservative. A new testing setup is proposed where thermal shocks are applied with a pulsed laser beam while the thermal and kinematic fields on the specimen surface are measured with infrared (IR) and visible cameras, respectively. Experimental testings are performed and different measurement techniques for temperature and kinematic fields are used. IR camera and pyrometers allow to measure the temperature variations in the zone impacted by the laser beam. To estimate the absolute temperature, the surface emissivities at the respective wavelengths are determined by different methods. The absolute temperature field is then used to apply the actual thermal loading in a decoupled FE model after an identification process of the parameters of the laser beam. Once the thermal loading is generated based upon the experimental data, the stress and strain fields can be computed in the region of interest with an elastoplastic law.The experimental strain variations calculated from the DIC measurements are compared with the predictions obtained with the FE simulation.

<p>Fracture of silicon solar cells in photovoltaic (PV) modules are widely reported and a wellknown issue in the PV industry, since it is exposed to adverse climatic conditions and varying temperature loads. A commercial silicon solar cell is mainly composed of four different layers. This thesis investigates delamination failure and thermal fatigue failure due to alternating temperature loads using finite element method (FEM) simulation.</p> <p><br></p> <p>The delamination of the encapsulant (EVA) layer and the cell interface was simulated using</p> <p>finite element (FE) simulations in the COMSOL Multiphysics software. The adhesion between the</p> <p>layers were modeled using the cohesive zone model (CZM). The CZM parameters such as normal</p> <p>strength and penalty stiffness were used for the bilinear traction-separation law for the cohesive</p> <p>model in a 90-degree configuration. The critical energy release rate (𝐺𝐺𝑐𝑐) was experimentally calculated as one of the CZM parameters. A uniaxial tensile test of the upper layer of the cell was conducted to determine the material properties of the solar cell layers, and that information was</p> <p>later used for FE simulations. To validate the simulation, we compared the peeling force graph</p> <p>from the experiment and FE simulation, and it was found both graphs showed a maximum peeling</p> <p>force of 120 N.</p> <p><br></p> <p>Finite element simulations were also conducted to predict the stress variations in the silicon</p> <p>solar cell layer due to alternating temperatures. An alternating temperature function was developed</p> <p>using triangular waveform equations in the COMSOL Multiphysics software. For this simulation,</p> <p>a 3D model of the cell with a 90-degree peel arm was used, like in the peeling simulation. A</p> <p>maximum stress of 7.31 x 10−3 𝑁/𝑚𝑚2 was observed on the encapsulant (EVA)/cell layer, but no</p> <p>delamination was observed for the given temperature range. In future work, we plan to explore the</p> <p>calculation of fatigue life using thermal simulation to predict the reliability of a solar cell.</p>

No description available.

The use of plastic materials in the design of vehicle components is primarily driven by the need for vehicle weight and cost reduction. Additionally, these materials give design engineers freedom in creating appealing exterior designs. However, creating self-carrying exterior structures with polymers must fulfill long-term strength, creep and fatigue life requirements. Thus, the polymer polyDicyclopentadiene (pDCPD) has been chosen for this purpose. Its aging mechanics need to be understood by the design engineers to make the right decisions. This thesis has carried out mechanical tests such as uniaxial tensile testing, fatigue, and creep testing. Digital image correlation (DIC) system has been used to capture strain data from tensile tests. In the final analysis, DIC measurements proved more accurate than extensometer data retrieved from the testing machine. The rise in temperature has been captured using thermal imaging. Several degradation processes have been explored including physical aging, thermo-oxidation, photo-oxidation, chemical- and bio- degradations. Test results showed significant changes in mechanical properties after 17 years of aging. Additionally, severe thermal degradation has been observed in one of the tested panels of pDCPD. Temperature can rise to significant levels during cyclic loading at high stresses, which could have an impact on physical aging effects. Viscoelastic behavior has been explored and changes in dynamic and creep properties have been observed. The investigation also reviled that different defects caused by flawed manufacturing also can affect the material severely as one case has proved in this research.

Utilizou-se o conceito de ?aço matriz + NbC? para produzir ligas com a matriz do aço rápido M2 ( 0,5%C ? 2%W ? 3%Mo ? 4,6%Cr ? 1%V) e variadas frações volumétricas de carbonetos de nióbio. Adicionou-se 2,5 e 5% de nióbio e carbono estequiométrico para a obtenção de carbonetos NbC e titânio (0,1%) para modificação da morfologia dos carbonetos NbC. Os carbonetos NbC apresentaram-se como carbonetos eutéticos com morfologia de escrita chinesa, como carbonetos primários com a morfologia de cruz de malta e como carbonetos eutéticos e primários com morfologia poligonal, estes últimos modificados com a adição de titânio. Após tratamento térmico de têmpera e revenimento para obtenção da máxima dureza, as ligas foram submetidas a ensaios de fadiga térmica (100 ciclos, 650ºC), de abrasão (roda de borracha ? 130N, 200rpm, 30min, hematita como abrasivo) e de deslizamento alternado (disco contra esfera ? 70,6N, amplitude: 6mm, freqüência, 6 Hz, 2h) para estudar o efeito da fração volumétrica e da morfologia dos carbonetos frente a estas solicitações. As ligas com carbonetos com morfologia poligonal e menor fração volumétrica de carbonetos (comparando-se morfologias iguais) apresentaram o melhor desempenho sob fadiga térmica devido ao baixo valor do parâmetro C/Dm da microestrutura (continuidade de carbonetos/distância livre média entre carbonetos). Os corpos-de-prova foram caracterizados por meio de microscopia ótica e eletrônica de varredura para determinar os sítios de nucleação e caminhos de propagação das trincas. Nos ensaios em roda de borracha as ligas com carbonetos eutéticos divorciados com morfologia poligonal apresentaram maior resistência ao desgaste do que os aços contendo carbonetos eutéticos cooperativos. O aumento da fração volumétrica de carbonetos NbC teve um máximo na resistência a abrasão e depois uma queda devido a presença de carbonetos primários grosseiros que fraturaram na superfície ensaiada e foram arrancados aumentanto a perda de massa. Nos ensaios de deslizamento alternado não foi possível hierarquizar o comportamento das ligas. Os corpos-de-prova de abrasão e de deslizamento foram caracterizados por microscopia ótica e eletrônica de varredura para determinar os mecanismos de desgaste atuantes. Um aço rápido para cilindros de laminação a quente (2%C ? 5%Cr ? 5%Mo ? 5%V) foi ensaiado sob condições idênticas às aplicadas às ligas estudadas, objetivando comparar desempenhos. O aço rápido apresentou desempenho superior nos ensaios de abrasão e de deslizamento alternado (devido a alta fração volumétrica de carbonetos eutéticos) e inferior no ensaio de fadiga térmica (devido ao alto parâmetro C/Dm da microestrutura oriundo da alta fração volumétrica de carbonetos eutéticos). / The concept of ?matrix steel + NbC? was used to cast alloys with the M2 steel matrix (0,5%C ? 2%W ? 3%Mo ? 4,6%Cr ? 1%V) and different volume fractions of niobium carbides. Niobium (2,5 e 5%) and stoichiometric carbon were added to produce NbC carbides and titanium (0,1%) to modify de NbC carbides morphology. NbC presented three basic morphologies: Chinese script (coupled eutectic); primary carbides with cross morphology and polygonal primary and eutectic carbides (divorced eutectics). After heat treatment of quench and temper in order to obtain the maximum hardness, the alloys were submitted to thermal fatigue test (100 cycles, 650ºC), dry rubber wheel abrasive wear test (130N, 200rpm, 30min, hematite as abrasive) and reciprocating sliding wear test (70,6N, amplitude: 6mm, frequency: 6Hz, 2h). The alloys with polygonal NbC carbides and lower volume fractions of carbides (for the same morphology) showed the best behaviour due to their low ?carbide continuity/carbide free path? ratio of the microstructure. The alloys were characterized by optical microscopy and SEM to investigate de cracks nucleation and propagation. In the dry rubber wheel tests, polygonal NbC eutectic carbides (divorced eutectics) showed better behaviour than Chinese script NbC eutectic carbides. High volume fractions of NbC carbides improved the abrasion resistance until a maximum and after that, the presence of big primary NbC carbides, lowered the abrasion resistance due to cracks in those big carbides. The results of the reciprocating sliding tests have not allowed to rank the performance of the alloys. Abrasion and sliding specimens were submitted to optical microscopy and SEM in order to evaluate the prevalent wear mechanisms. One high speed steel for hot rolling mill rolls (2%C ? 5%Cr ? 5%Mo ? 5%V) was tested under the same conditions that the alloys studied were tested in order to compare their performances. The high speed steel showed better performance in abrasion and reciprocating sliding wear due to the high volume fraction of coupled eutectic carbides and lower performance in thermal fatigue due to the high ?carbide continuity/carbide free path? ratio of the microstructure than the alloys studied.

<p>In powder metallurgy research field, Direct Metal Laser Sintering (DMLS) and Metal Powder Starch Consolidation (MPSC) are relatively new rapid forming techniques to fabricate complex and near net-shaped components. The working principles of DMLS are to melt and fuse metal powder layer by layer in computer controlled systems to pile up components like three dimensional printing. It has been for instance extensively used for mould inserts, die parts, and functional metal prototypes. Another, less explored method, starch consolidation is a pressureless direct casting method which consists principally of mixing powder slurry, casting into moulds, consolidation, drying, and sintering. With a strong focus on both methods, the study here combines several strong material technology sectors; powder, rapid forming, mechanical property testing and surface technology. It covers the processing chain from green body preparation, optimization of</p><p>sintering, nitriding, post sinter heat treatment, to modeling and assessment of material behaviour for end-user applications. An iron based powder and a high vanadium high speed steel powder with low and high carbon contents were used in the DMLS and MPSC processes, respectively. The overall aim of the study is to synthesize near net-shaped powder-based components, to characterize pores and microstructure, and to establish a fundamental understanding of failure mechanisms of powder based materials in bending fatigue, thermal fatigue and wear.</p><p>The study showed the DMLS and MPSC technologies could produce shaped components with a multi-phased structure, controllable nitriding depth and high relative densities in a range of 97 - 99.7 %. Materials' heterogeneity and porosity have detrimental influence on mechanical properties, especially on crack initiation and subsequent propagation.</p>

This study investigates the reliability of SnPb and SnAg solder joints in semiconductor packages subjected to thermal cycling. More specifically, solder joint crack growth and life are experimentally measured, and FEM models are run to explain the test results. Ultimately a life-prediction model is proposed for both SnPb and SnAg solder joint packages. Motorola 357-plastic ball grid array packages on printed wiring boards were thermal cycled with the following test parameters: SnPb and SnAg solders, three post-process conditions (aged, aircooled and quenched), four package layouts on the printed circuit boards (singledense, single-sparse, double-alternating, and double-dense), three accelerated thermal cycling protocols (0°C to 100°C, -40°C to 125°C, and -55°C to 125°C), and tests run at Motorola and the University of Texas. At predetermined thermal cycles, packages were removed from the environmental chambers, dyepenetrated, packages removed to expose the solder joints, and optical images taken. Images were processed to measure crack area, shape, orientation and length to show crack growth. Selected joints were sectioned and polished to investigate microstructure and failure modes. Selected boards were connected to an ANATECH event detector to monitor life from joint failures. FEM crack initiation and propagation models were developed to better understand failure mechanisms. Major experimental results are: 1) SnPb joints have about 50% faster crack growth rates than SnAg joints, subsequently SnPb joints have half the life of SnAg joints, 2) air-cooled and quenched packages had similar failure characteristics, but aged SnPb joints had lower life and aged SnAg joints had significantly longer life than the comparable nonaged joints, 3) double-dense package layout significantly decreased life (by 75%) over the other package layouts, which were similar to each other, 4) the test results at the two locations (UT and Motorola) were similar for SnPb solder joints, but significantly different for SnAg solder joints, and 5) the largest cracks occurred at the corners of joints just under the die edge. Major FEM simulation results are: 1) the crack initiation life of SnAg joints is approximately 100% longer than SnPb joints, 2) shear load is a major cause of crack growth, but the contribution of tensile load increases as the cracks grow, 3) primary cracks at the board interface appear to reduce the propagation rate of the primary crack on the package interface, 4) secondary cracks are suppressed when compressive stresses prevent voids from nucleating, 5) the double-dense configuration shows no PWB warping due to symmetry, and its stresses are larger than for the other package layouts, and (6) the stresses and strains for single-dense, single-sparse, and double-alternating package layouts are similar because the stresses/strains are dominated by local effects due to the CTE mismatch between the die and board. Based upon the experimental results and FEM simulations, a lifeprediction model based upon a severity metric was proposed. The metric estimates damage to the solder joints and links material properties and parameters associated with package layout and thermal test conditions to the time-dependent creep, time-independent plastic deformation, and a time-dependent and geometric effective stress of the solder. The severity metric predicted life very well for most of the data tested and was more accurate than the industry-standard life-prediction models for SnPb solder joints.

Εξ’ αιτίας της ραγδαίας αύξησης στη χρήση σύνθετων υλικών, στην παρούσα εργασία ασχοληθήκαμε με σύνθετο υλικό μήτρας εποξικής ρητίνης και ενίσχυσης κόκκους αλουμινίου με μέση διάμετρο 63 μm. Σκοπός της έρευνας αυτής είναι κατά πρώτον να μελετήσει τη συμπεριφορά του συνθέτου σε στατική κάμψη αναλόγως της κατά βάρος περιεκτικότητά του σε κόκκους και να συγκρίνει τα πειραματικά αποτελέσματα με αντίστοιχες θεωρητικές προβλέψεις και κατά δεύτερον να μελετήσει την επίδραση βλάβης λόγω ύπαρξης εγκοπής ή θερμικής κόπωσης στην υποβάθμιση του σύνθετου υλικού και να προβλέψει την παραμένουσα μηχανική συμπεριφορά χρησιμοποιώντας το μοντέλο R.P.M. Τρία διαφορετικά μοντέλα πρόβλεψης, ανεπτυγμένα απ’ το CMG (Composite Material Group) του Πανεπιστημίου Πατρών, θα εφαρμοστούν για τις προβλέψεις και δύο απ’ αυτά θα συγκριθούν και με άλλα μοντέλα ανεπτυγμένα από άλλους ερευνητές. Κατ’ αρχήν, για τον υπολογισμό της μέγιστης τάσης εφαρμόστηκε το μοντέλο του τμηματικού κόκκου. Σύμφωνα με το μοντέλο αυτό, ο κόκκος χωρίζεται σε άπειρο αριθμό ινών και σύμφωνα με την θεωρία του Cox μπορεί να υπολογιστεί η μέση τάση που ασκείται σε κάθε ίνα του κόκκου. Στη συνέχεια, για τον υπολογισμό του μέτρου ελαστικότητας συναρτήσει της κατά βάρους περιεκτικότητας σε κόκκους αλουμινίου εφαρμόστηκε το μοντέλο της μεσοφάσης. Το μοντέλο αυτό λαμβάνει υπόψιν την ύπαρξη μιας τρίτης φάσης ανάμεσα στις δύο κύριες (μήτρα-ενίσχυση) και η οποία αποτελεί μια σημαντική παράμετρο επίδρασης στη συμπεριφορά οποιουδήποτε σύνθετου υλικού. Τέλος, στις περιπτώσεις της ύπαρξης εγκοπής και της θερμικής κόπωσης εφαρμόστηκε το μοντέλο R.P.M. Το μοντέλο αυτό μπορεί να εφαρμοστεί για την περιγραφή της υποβάθμισης των ιδιοτήτων των υλικών μετά από βλάβη και στη συγκεκριμένη εργασία εφαρμόστηκε για να περιγράψει τις μεταβολές στην μέγιστη τάση του υλικού και στο μέτρο ελαστικότητάς του συναρτήσει του μήκους εγκοπής ή του αριθμού των θερμικών κύκλων. / -

In powder metallurgy research field, Direct Metal Laser Sintering (DMLS) and Metal Powder Starch Consolidation (MPSC) are relatively new rapid forming techniques to fabricate complex and near net-shaped components. The working principles of DMLS are to melt and fuse metal powder layer by layer in computer controlled systems to pile up components like three dimensional printing. It has been for instance extensively used for mould inserts, die parts, and functional metal prototypes. Another, less explored method, starch consolidation is a pressureless direct casting method which consists principally of mixing powder slurry, casting into moulds, consolidation, drying, and sintering. With a strong focus on both methods, the study here combines several strong material technology sectors; powder, rapid forming, mechanical property testing and surface technology. It covers the processing chain from green body preparation, optimization of sintering, nitriding, post sinter heat treatment, to modeling and assessment of material behaviour for end-user applications. An iron based powder and a high vanadium high speed steel powder with low and high carbon contents were used in the DMLS and MPSC processes, respectively. The overall aim of the study is to synthesize near net-shaped powder-based components, to characterize pores and microstructure, and to establish a fundamental understanding of failure mechanisms of powder based materials in bending fatigue, thermal fatigue and wear. The study showed the DMLS and MPSC technologies could produce shaped components with a multi-phased structure, controllable nitriding depth and high relative densities in a range of 97 - 99.7 %. Materials' heterogeneity and porosity have detrimental influence on mechanical properties, especially on crack initiation and subsequent propagation.

Utilizou-se o conceito de ?aço matriz + NbC? para produzir ligas com a matriz do aço rápido M2 ( 0,5%C ? 2%W ? 3%Mo ? 4,6%Cr ? 1%V) e variadas frações volumétricas de carbonetos de nióbio. Adicionou-se 2,5 e 5% de nióbio e carbono estequiométrico para a obtenção de carbonetos NbC e titânio (0,1%) para modificação da morfologia dos carbonetos NbC. Os carbonetos NbC apresentaram-se como carbonetos eutéticos com morfologia de escrita chinesa, como carbonetos primários com a morfologia de cruz de malta e como carbonetos eutéticos e primários com morfologia poligonal, estes últimos modificados com a adição de titânio. Após tratamento térmico de têmpera e revenimento para obtenção da máxima dureza, as ligas foram submetidas a ensaios de fadiga térmica (100 ciclos, 650ºC), de abrasão (roda de borracha ? 130N, 200rpm, 30min, hematita como abrasivo) e de deslizamento alternado (disco contra esfera ? 70,6N, amplitude: 6mm, freqüência, 6 Hz, 2h) para estudar o efeito da fração volumétrica e da morfologia dos carbonetos frente a estas solicitações. As ligas com carbonetos com morfologia poligonal e menor fração volumétrica de carbonetos (comparando-se morfologias iguais) apresentaram o melhor desempenho sob fadiga térmica devido ao baixo valor do parâmetro C/Dm da microestrutura (continuidade de carbonetos/distância livre média entre carbonetos). Os corpos-de-prova foram caracterizados por meio de microscopia ótica e eletrônica de varredura para determinar os sítios de nucleação e caminhos de propagação das trincas. Nos ensaios em roda de borracha as ligas com carbonetos eutéticos divorciados com morfologia poligonal apresentaram maior resistência ao desgaste do que os aços contendo carbonetos eutéticos cooperativos. O aumento da fração volumétrica de carbonetos NbC teve um máximo na resistência a abrasão e depois uma queda devido a presença de carbonetos primários grosseiros que fraturaram na superfície ensaiada e foram arrancados aumentanto a perda de massa. Nos ensaios de deslizamento alternado não foi possível hierarquizar o comportamento das ligas. Os corpos-de-prova de abrasão e de deslizamento foram caracterizados por microscopia ótica e eletrônica de varredura para determinar os mecanismos de desgaste atuantes. Um aço rápido para cilindros de laminação a quente (2%C ? 5%Cr ? 5%Mo ? 5%V) foi ensaiado sob condições idênticas às aplicadas às ligas estudadas, objetivando comparar desempenhos. O aço rápido apresentou desempenho superior nos ensaios de abrasão e de deslizamento alternado (devido a alta fração volumétrica de carbonetos eutéticos) e inferior no ensaio de fadiga térmica (devido ao alto parâmetro C/Dm da microestrutura oriundo da alta fração volumétrica de carbonetos eutéticos). / The concept of ?matrix steel + NbC? was used to cast alloys with the M2 steel matrix (0,5%C ? 2%W ? 3%Mo ? 4,6%Cr ? 1%V) and different volume fractions of niobium carbides. Niobium (2,5 e 5%) and stoichiometric carbon were added to produce NbC carbides and titanium (0,1%) to modify de NbC carbides morphology. NbC presented three basic morphologies: Chinese script (coupled eutectic); primary carbides with cross morphology and polygonal primary and eutectic carbides (divorced eutectics). After heat treatment of quench and temper in order to obtain the maximum hardness, the alloys were submitted to thermal fatigue test (100 cycles, 650ºC), dry rubber wheel abrasive wear test (130N, 200rpm, 30min, hematite as abrasive) and reciprocating sliding wear test (70,6N, amplitude: 6mm, frequency: 6Hz, 2h). The alloys with polygonal NbC carbides and lower volume fractions of carbides (for the same morphology) showed the best behaviour due to their low ?carbide continuity/carbide free path? ratio of the microstructure. The alloys were characterized by optical microscopy and SEM to investigate de cracks nucleation and propagation. In the dry rubber wheel tests, polygonal NbC eutectic carbides (divorced eutectics) showed better behaviour than Chinese script NbC eutectic carbides. High volume fractions of NbC carbides improved the abrasion resistance until a maximum and after that, the presence of big primary NbC carbides, lowered the abrasion resistance due to cracks in those big carbides. The results of the reciprocating sliding tests have not allowed to rank the performance of the alloys. Abrasion and sliding specimens were submitted to optical microscopy and SEM in order to evaluate the prevalent wear mechanisms. One high speed steel for hot rolling mill rolls (2%C ? 5%Cr ? 5%Mo ? 5%V) was tested under the same conditions that the alloys studied were tested in order to compare their performances. The high speed steel showed better performance in abrasion and reciprocating sliding wear due to the high volume fraction of coupled eutectic carbides and lower performance in thermal fatigue due to the high ?carbide continuity/carbide free path? ratio of the microstructure than the alloys studied.