Zoheir N. Farhat

The Role of Reversible Martensitic Transformation in the Wear Process of TiNi Shape Memory Alloy

It has been established that the superelastic effect of TiNi alloy is related to a reversible martensitic transformation; that is, stress-induced transformation. The high elastic recovery of TiNi alloy has made it a potential candidate for high wear resistance applications. In the present study the tribological behavior of superelastic TiNi alloy was studied and compared to Ni, Ti, and AISI 304 stainless steel using dry sliding wear and friction tests. The effect of normal load and testing temperature on superelasticity has been investigated. It has been found that although AISI 304 stainless steel and superelastic TiNi alloy have similar hardness, TiNi exhibits superior wear resistance. The wear rate of AISI 304 stainless steel is over four times higher than TiNi. The superior wear resistance of TiNi and the effect of load and temperature on wear were discussed and related to the reversible martensitic phase transformation, as well as self-accommodation and stabilization of martensite.

Dent Resistance and Effect of Indentation Loading Rate on Superelastic TiNi Alloy

The large recoverable deformation associated with reversible stress-induced martensitic transformation for superelastic TiNi alloys has been widely exploited in many applications. However, to employ superelastic TiNi in applications where high impact loading is expected, as in bearings, the effect of loading rate on superelasticity needs to be understood. In the current article, the effect of indentation loading rate on dent resistance and superelasticity of TiNi is studied. Indentation tests are performed, at different loading rates on superelastic TiNi alloy and correlated to tensile stress–strain data. It is found that the reversible deformation drops as loading rate is increased and superelasticity diminishes. Based on data collected and results analysis it is proposed that the loss in superelastic behavior under high indentation loading rate is related to retardation of the stress-induced martensitic transformation. Furthermore, a simple heat model was proposed and showed that the temperature rise during indentation is not significant.

Reciprocating wear response of Ti(C,N)–Ni3Al cermets

Abstract Ti(C,N) based cermets have received significant attention due to their enhanced mechanical properties at elevated temperatures, low mass and increased chemical stability, when compared to WC–Co hardmetals. These properties have been found to be superior in many cases to traditional hardmetal replacements, such as TiC–Ni. The current study focuses on Ti(C,N)–Ni3Al cermets formed through melt infiltration (with binder contents ranging from 20 to 40 vol.-%Ni3Al). Comparison is made with TiC–Ni3Al cermets using an identical binder alloy. The reciprocating ball on flat wear properties of the cermets were evaluated as a function of applied load (using a WC–Co counterface), together with the composite hardness and indentation fracture resistance. It is shown that nitrogen content negatively affects infiltration, resulting in non-infiltrated areas within low binder content cermets, which decreases the indentation fracture resistance and hardness. This problem can be largely mitigated by increasing binder content. When comparing fully infiltrated cermets, increasing nitrogen content decreases hardness and increases toughness, while all Ti(C,N) cermets outperform TiC (at 40 vol.-% binder). Reciprocating wear increased with increasing load, and typically was the most severe for the lowest binder contents. A combination of wear mechanisms were apparent, including both abrasive and adhesive wear, with the formation of an oxide tribolayer containing components from both the tested cermets and the WC–Co counterface material. Les cermets à base de Ti(C,N) ont reçu une attention importante grâce à leurs propriétés mécaniques améliorées aux températures élevées, à leur faible masse et à leur stabilité chimique augmentée, lorsque comparés aux carbures métalliques de WC–Co. Dans plusieurs cas, on a trouvé que ces propriétés étaient supérieures à celles des remplacements traditionnels de carbures métalliques, comme le TiC–Ni. La présente étude se concentre sur les cermets de Ti(C,N) –Ni3Al formés par infiltration du bain (la teneur du liant variant de 20 à 40% en volume de Ni3Al). On les compare aux cermets de TiC–Ni3Al en utilisant un alliage de liaison identique. On a évalué les propriétés d’usure par déplacement alternatif de bille sur disque des cermets en fonction de la charge appliquée (utilisant un antagoniste en WC–Co), ainsi que de la dureté du composite et de la résistance à la fracture d’indentation. On montre que la teneur en azote affecte négativement l’infiltration, ayant pour résultat des régions non infiltrées à l’intérieur des cermets à faible teneur en liant, ce qui diminue la résistance à la fracture d’indentation et la dureté. On peut largement atténuer ce problème en augmentant la teneur en liant. Lorsque l’on compare des cermets entièrement infiltrés, l’augmentation de la teneur en azote diminue la dureté et augmente la ténacité, alors que tous les cermets de Ti(C,N) surpassent le TiC (à 40% en volume de liant). L’usure par déplacement alternatif augmentait avec une augmentation de la charge, et était typiquement plus sévère pour les plus faibles teneurs en liant. Une combinaison de mécanismes d’usure était apparente, incluant tant l’usure par abrasion que l’usure d’adhérence, avec formation d’une couche tribologique oxyde contenant des composantes tant des cermets évalués que du matériau antagoniste en WC–Co.

Slurry Erosion of Pipeline Steel: Effect of Velocity and Microstructure

Pipelines are the most flexible, economic, and convenient way for oil and gas transportation. Material degradation by slurry erosion is a common feature in oil transmission pipeline. In the present work, slurry erosion of AISI 1018, AISI 1080, API X42, and API X70 steels is investigated in terms of slurry velocity and target material microstructure. The slurry velocity and impact angle employed were 0.2, 0.29, 0.36, and 0.43 m s−1 and 90 deg, respectively. It is found that erosion rate increases with increasing slurry velocity. Scanning electron microscopy was employed to investigate the eroded surface and subsurface of the steels. Plastic deformation, microcutting, and fracture are identified as dominant erosion mechanisms. Pearlitic microstructure exhibits superior erosion resistance compared to ferrite depending upon slurry velocity and microstructural orientation.

Reciprocating Wear Behavior of Al Alloys: Effect of Porosity and Normal Load

Aluminum alloys are attractive for critical applications such as pistons, clutch housings and liners in automotive industry for their high strength to weight ratio, high corrosion resistance and good heat conductivity. These alloys can be fabricated using casting and powder metallurgy techniques in which porosity is a common feature. The presences of pores adversely affect the mechanical properties and wear resistance of these components. Not only the total area percentage of porosity influences the degradation in properties but also size, shape and interconnectivity of pores play an important role. In this study, aluminum alloys were produced using powder metallurgy technique. The amount of porosity was varied by varying compaction pressure and amount of wax added before compaction. Reciprocating wear tests (ball-on-flat configuration) were performed against AISI 52100 bearing steel ball under both low (1.5- 5N) and high (6-20N) loads. Scanning electron microscopy was employed in order to identify possible wear mechanisms. Both detrimental and beneficial effects of porosity under different loading conditions were observed. An attempt has been made to develop a relationship between pore size and distribution and wear behavior of aluminum alloys.

Recent advances in electroless-plated Ni-P and its composites for erosion and corrosion applications: a review

The metallic coating of surfaces plays a vital role in the protection of most industrial applications. Coatings can be carried through various routes (e.g., mechanical and electrochemical plating techniques). Electroless nickel coatings present unparalleled properties and a unique combination of corrosion and wear resistance features. Recently, the use and development of electroless nickel-phosphorus (ENP) coatings has attracted broad attention from many industries (e.g., oil and gas) due to their superior corrosion and wear resistance properties. In the present review article, mechanisms of ENP and preparation methods are briefly outlined. The review sheds light on properties of electroless Ni-P coatings and of their nanocomposites with an emphasis on new products and on their future development.

The effects of Ni3Al binder content on the electrochemical response of melt-infiltration processed TiC–Ni3Al cermets

TiC–Ni3Al samples were successfully fabricated with varying amounts of the Ni3Al intermetallic binder (alloy IC-50), ranging from 10 to 40 wt-%, through a simple melt-infiltration method. Each sample was then tested to determine the degree of resistance of that composition to electrochemical corrosion in an aqueous solution containing 3.5 wt-% NaCl, using a range of testing procedures including open-circuit potential, potentiodynamic polarisation and cyclic polarisation. Results indicate that the lowest binder content results in greater potential to resist corrosion. It is demonstrated that the Ni3Al binder undergoes dissolution for the examined conditions, which was confirmed through the high amount of Al and Ni in the electrolyte solutions following testing. It was also confirmed from the electrochemical experiments and the SEM that localised corrosion was visible.

Prediction of Indentation Behavior of Superelastic TiNi

Superelastic TiNi shape memory alloys have been extensively used in various applications. The great interest in TiNi alloys is due to its unique shape memory and superelastic effects, along with its superior wear and dent resistance. Assessment of mechanical properties and dent resistance of superelastic TiNi is commonly performed using indentation techniques. However, the coupling of deformation and reversible martensitic transformation of TiNi under indentation conditions makes the interpretation of results challenging. An attempt is made to enhance current interpretation of indentation data. A load-depth curve is predicted that takes into consideration the reversible martensitic transformation. The predicted curve is in good agreement with experimental results. It is found in this study that the elastic modulus is a function of indentation depth. At shallow depths, the elastic modulus is high due to austenite dominance, while at high depths, the elastic modulus drops as the depth increases due to austenite to martensite transition, i.e., martensite dominance. It is also found that TiNi exhibits superior dent resistance compared to AISI 304 steel. There is two orders of magnitude improvement in dent resistance of TiNi in comparison to AISI 304 steel.