High Temperature Hardness Research Articles

Improved high-temperature hardness and wear resistance of Inconel 625 coatings fabricated by laser cladding

In this study, Inconel 625 coatings were fabricated by laser cladding and shielded metal arc welding, and the microstructure, hardness and wear resistance at both room and elevated temperatures are investigated. The results indicate that laser cladded Inconel 625 coating has finer microstructure, alleviated segregation of Mo and Nb and lower dilution of iron compared with arc welded one as revealed by XRD, SEM and EDS results. The hardness profile at room temperature can be divided into four regions, namely coating zone, iron dilution zone, heat affected zone and substrate. Laser cladded Inconel 625 coating has slightly higher hardness in coating zone, whereas much higher hardness in iron dilution zone, indicating that iron distribution plays important role in the hardness. At elevated temperatures, the hardness of laser cladded Inconel 625 coating is higher due to finer microstructure and alleviated segregation. The wear test results show that abrasive wear is apparent at room temperature, whereas adhesive wear is dominant at elevated temperature. In comparison, laser cladded coating has lower wear rate because of lower dilution of iron and higher hardness. Therefore, laser cladded Inconel 625 coating is preferred due to its better mechanical performance at both room and elevated temperature.

On The Superior High Temperature Hardness of Precipitation Strengthened High Entropy Ni‐Based Alloys

The microstructure and high temperature hardness of two face‐centered cubic high entropy Ni‐based alloys with L12 γ′ precipitates have been studied. Both alloys exhibit higher mixing entropy and with the advantages in lower density and lower cost of raw materials than conventional Ni‐based superalloys. Their γ′ solvus are above 1 150 °C, and the γ–γ′ microstructure can be thermodynamically stable after isothermal ageing from 700 to 1 100 °C for at least 500 h. By XRD peak deconvolution, positive lattice misfits between γ and γ′ have been shown till elevated temperatures. The results from nano‐indentation test indicate that their highly alloyed γ′ phase have rendered more significant strengthening, and the underlying mechanism can be attributed to the higher anti‐phase boundary energy. Therefore, with minor refractory additions, the bulk hardness of present alloys can surpass that of commercial superalloy from room to high temperature.

Introduction of a novel tribometer especially designed for scratch, adhesion and hardness investigation up to 1000℃

In order to gain a fundamental understanding of material behaviour at elevated temperatures a unique tribometer was designed which can operate at temperatures up to 1000℃. The test takes place in vacuum in order to avoid oxidation and the normal load range varies from 10 to 500 N. It is thus possible to describe the evolution of hardness over a broad range of temperatures and loads. This can give indications of possible microstructural modifications, which can be investigated afterwards on cross sections. For the characterisation of single abrasive phenomena on a very fundamental level, scratch tests at variable loads are proposed. The interaction of sliding surfaces can be simulated by adhesion testing. To this end an application specific counter body, e.g. taken from a field specimen, can be slid over the specimen surface at variable loads. Finally, it can be stated that this newly designed tribometer offers an enormous potential for deeper understanding of fundamental wear phenomena like ploughing, micro-breaking or adhesion occurring at high temperature. The possibilities of high temperature scratch and hardness testing with the new measurement system are shown on the common austenitic stainless steel 1.4301 (AISI 304).

High temperature hardness of steels and iron-based alloys

Hot hardness, related to the mechanical strength and wear resistance of materials at high temperatures, has been measured from room temperature up to 800°C for a comprehensive set of iron-based alloys having different microstructures and chemical compositions. The results obtained suggest the existence of several softening regimes with increasing temperatures, also with a massive hardness drop observed to begin at temperatures close to 0.5 times the melting temperature for most of the chosen alloys. Austenitic steel grades were also observed to show a significant softening behaviour at moderate temperatures compared to ferritic and martensitic alloys, attributed to the dislocation dynamics of face cubic centred alloys. The exact nature of the temperature dependence shown by hardness has been proposed to adopt the form of an exponential Arrhenius equation. Another model suggested in the available literature is also discussed within this context. Additionally, the role of alloying elements has been correlated to the softening behaviour. Molybdenum or boron were found to slow down the softening behaviour, while carbide-forming elements such as vanadium and tungsten were found to be beneficial for room temperature hardness.

SiC detector damage and characterization for high intensity laser-plasma diagnostics

Silicon-Carbide (SiC) detectors are always more extensively employed as diagnostics in laser-generated plasma due to their remarkable properties such as their high band gap, high carrier velocity, high detection efficiency, high radiation resistance and low leakage current at room temperature. SiC detectors, in comparison with Si detectors, have the advantage of being insensitive to visible light, having low reverse current at high temperature and high radiation hardness. A similar energy resolution characterizes the two types of detectors, being 0.8% in Si and 1.0% in SiC, as measured detecting 5.8 MeV alpha particles. Generally, SiC detectors are employed as laser-plasma diagnostics in time-of-flight configuration, permitting the simultaneous detection of photons, electrons and ions based on discrimination of velocity. SiC detectors can be employed in the proportionality regime, because their response is proportional to the radiation energy deposited in the active layer. Using thin absorbers in front of the detectors makes it possible to have further information on the radiation nature, intensity and energy. Surface characterization of SiC before and after prolonged exposure to hot plasma laser generated shows the formation of bulk defects and thin film deposition on the detector surface limiting the device functionality.

Studying High-Temperature Hardness of Powder Cobalt Alloys Strengthened with Niobium or Titanium Carbides

The hardness of cobalt powder alloys in the ‘room temperature–1150°C’ temperature range is investigated. The alloys are prepared by hot pressing of cobalt, chromium, aluminum, and iron powders with titanium or niobium carbides. The hardness of the alloys strengthened with 30 to 50 vol.% carbide at various temperatures show that the amount of the strengthening phase affects the hardness of the alloys investigated. The most significant factor that affects the hardness of the alloys is the temperature factor: with increasing temperature the hardness reduces regardless of the type and content of the carbides. It is shown that the hardness of the alloys with titanium carbide exceeds the hardness of those with niobium carbide. These results could be used to create friction materials for aviation purposes.

High temperature three-body abrasive wear of 0.25C 1.42Si steel with carbide free bainitic (CFB) and martensitic microstructures

In the present work, the wear behaviour of different steels has been investigated under a three body abrasive environment at room and elevated temperatures. High-silicon steel (0.25C–1.42Si) was austempered at 300 and 320°C in order to obtain two carbide-free bainitic steels with different mechanical properties. The same steel subjected to two different quench and temper heat treatments was used as a reference material for mechanical and wear testing. The steels were subjected to three-body abrasive wear by means of a high temperature continuous abrasion tester (HT-CAT). The tests were done at 25, 300 and 500°C respectively. All samples showed similar wear rates at room temperature. At 500°C, the material austempered at 320°C showed the highest toughness and the lowest wear rate. High temperature hardness and impact toughness tests showed that abrasive wear is not only influenced by hardness but also by the toughness of the material. Owing to their good strength/toughness combination CFB steels could prove to be an important material for abrasive wear applications.

A Heat-Resistant NiCo0.6Fe0.2Cr1.5SiAlTi0.2 Overlay Coating for High-Temperature Applications

This paper proposes an overlay coating based on the high-entropy alloy composition NiCo0.6Fe0.2Cr1.5SiAlTi0.2 [high-entropy alloy coating (HEAC)]. HEAC samples underwent spark-plasma sintering processes and were subjected to oxidation tests, high-temperature hardness tests, and thermal conductivity and thermal expansion measurements. Experimental results indicated that the HEAC can form protective α-Al2O3 at 1100°C and exhibits oxidation behavior similar to that of MCrAlY. Furthermore, compared to MCrAlY, the HEAC possesses better thermal stability, higher hot hardness, lower thermal conductivity, and smaller thermal expansion. The potential of the HEAC as an overlay coating for high-temperature applications is discussed.

Tool life and wear mechanisms during Alloy 625 face milling

Nickel-based alloys, particularly Alloy 625, are very important materials which have been increasingly used in applications that require wear resistance, particularly in the oil and gas industries. One of their characteristics is low machinability, which is due to their combined properties of high-temperature hardness, mechanical strength, and corrosion and wear resistance. These properties mean that low cutting speeds are needed in order to increase tool life, although this is not always achieved. The main goal of this work is to evaluate different cemented carbide grades, cutting speeds, and feed per tooth rates, aiming to determine the best condition for face milling of nickel-based 625 superalloy. The tool life performance of the cutting tools and the wear mechanisms were analyzed based on the results of milling tests using a cutter with cemented carbide inserts. The main results indicate that tool wear mechanisms in the Alloy 625 milling are similar to those that occur in other nickel-based superalloys, such as 718 and 713. However, the wear rate is lower and there is evidence of occurrence of oxidation wear.

Influence of NbC and VC on microstructures and mechanical properties of WC–Co functionally graded cemented carbides

Functionally graded cemented carbides (FGCCs) usually have a coarse-grained surface layer. In order to refine the grain size of WC and to improve the mechanical properties, VC and NbC as grain growth inhibitors, were added to WC–6Co FGCCs. The grain growth kinetics of WC was investigated, and both the room temperature and high temperature mechanical properties were tested. The results show that the additions of NbC and VC reduce the thickness of the gradient layer in FGCCs. The addition of VC reduces the thickness of the gradient layer by half, while that of NbC is less effective. The additions of NbC and VC refine the grain size by suppressing the adsorption/desorption processes of WC grains in Co phase during the pre-sintering and the carburizing processes, and VC is more effective than NbC. The addition of NbC increases the transverse rupture strength of FGCCs, because of the fine microstructure, and the solution strengthening in Co phase. Both the additions of NbC and VC increase the high temperature hardness of FGCCs due to improved oxidation resistance, more homogeneous and finer microstructures.

Evaluation of high-temperature Vickers hardness using instrumented indentation system

Instrumented indentation testing is more advanced than conventional hardness testing in measuring various mechanical properties of materials. To evaluate these mechanical properties, information about indentation contact area is required. In particular, the deformation behavior of metals at high-temperatures seems to differ from that at room temperature, and thus for accurate evaluation of mechanical characteristics at high-temperatures, the high-temperature contact area should be used. In this study, an instrumented indentation system for high-temperatures was developed and measurement-errors caused by equipment temperature were calibrated. In addition, the pileup effect during indentation was studied at different temperatures. A new equation for the high-temperature contact area is proposed. For verification, conventional hardness testing was performed to compare the results with high-temperature instrumented indentation testing.

Designing high-temperature steels via surface science and thermodynamics

Electricity in many countries such as the US and China is produced by burning fossil fuels in steam-turbine-driven power plants. The efficiency of these power plants can be improved by increasing the operating temperature of the steam generator. In this work, we adopted a combined surface science and computational thermodynamics approach to the design of high-temperature, corrosion-resistant steels for this application. The result is a low-carbon ferritic steel with nanosized transition metal monocarbide precipitates that are thermally stable, as verified by atom probe tomography. High-temperature Vickers hardness measurements demonstrated that these steels maintain their strength for extended periods at 700°C. We hypothesize that the improved strength of these steels is derived from the semi-coherent interfaces of these thermally stable, nanosized precipitates exerting drag forces on impinging dislocations, thus maintaining strength at elevated temperatures.

Effect of gamma irradiation on high temperature hardness of low-density polyethylene

Gamma irradiation can cause the change of microstructure and molecular structure of polymer, resulting in the change of mechanical properties of polymers. Using the hardness measurement, the effect of gamma irradiation on the high temperature hardness of low-density polyethylene (LDPE) was investigated. The gamma irradiation caused the increase in the melting point, the enthalpy of fusion, and the portion of crystallinity of LDPE. The Vickers hardness of the irradiated LDPE increases with increasing the irradiation dose, annealing temperature, and annealing time. The activation energy for the rate process controlling the reaction between defects linearly decreases with the irradiation dose. The process controlling the hardness evolution in LDPE is endothermic because LDPE is semi-crystalline.

Research on Dynamic Recrystallization Behavior of Extra-Heavy Backup Roll Forming Process

Heavy backup roll is a key part of steckel mill, because of its exceptional work environment, it needs high temperature resistance, fracture resistance, hardness, toughness and other aspects of performance. The fine equiaxed grains can be got by repeated dynamic recrystallization and deformation. There is a high density of dislocations and dislocation tangles in material, which can improve the microstructure and properties of material.

Laboratory Study of Water Shutoff by Activated Heavy Oil for High Temperature and High Salinity Reservoirs

Abstract Activated heavy oil is a favorable blocking agent, because of its good selectivity and recyclability. In this paper, by simulating the reservoir conditions of Tahe Oilfield, the feasibility of water shutoff by activated heavy oil for high temperature, high salinity and high hardness reservoirs has been studied. Based on the reservoir characteristics, a nonionic-anionic compound emulsifier of 2 % MZ-18 + 3 % BH-12 (MZ-18 = nonionic amide emulsifier condensed by long chain carboxylic acid and polyethylene polyamine; BH-12 = anionic sulfonate emulsifier) was screened out as the optimum emulsification system for the activated heavy oil. The W/O emulsion prepared by the activated heavy oil is of high viscosity; besides, its temperature resistance, salinity tolerance and thermal stability were competent to Tahe reservoir. The water shutoff performance of activated heavy oil was evaluated by the physical simulation experiments. The results show that the activated heavy oil can improve the water shutoff performance and flushing resistance performance in a wide range of permeability – from 300 to 1 500 mD. Also it is found that, the water shutoff ability of the activated heavy oil increases with the increase of permeability of the sands, injection rate of blocking agent as well as the displacing rate of displacement fluid.

Ageing resistance of SiBCN ceramics

Amorphous SiBCN alloys are known – depending on the elemental composition – for their thermal stability and high-temperature (up to 1500°C) oxidation resistance, hardness, optical transparency or electrical and/or thermal conductivity. The paper reports ageing of SiBCN ceramics prepared in the form of thin films in a wide range of elemental compositions and preparation conditions. I focus on the room-temperature oxidation resistance, expressed in terms of the thickness and properties of the surface oxide layer 12 years since the deposition. I identify which compositions exhibit perfect long-time room-temperature oxidation resistance (this includes those, but not only those, which exhibit short-time high-temperature oxidation resistance) and which do not. For the latter I discuss the complex relationships between the characteristics of the surface oxide layer, the elemental composition of the films and the ion bombardment during the film growth. The results are important for tailoring long-lifetime ceramics combining the aforementioned functional properties.

A fractographical approach to the sintering process in porous ZrB2–B4C binary composites

Due to their high temperature stability and hardness, ZrB2–B4C composites have drawn attention of researchers in recent years. Although several studies have been conducted on the properties of ZrB2–B4C composites at high sintering temperatures (>2200°C), there is little information about their sintering process and densification at temperatures below 1850°C, which is industrially more attractive and could result in desirable porosity. In this paper, sintering process and porosity of ZrB2–B4C binary composites containing 0 to 100vol% B4C (hot pressed at 1800°C for 30min under a uniaxial load of 12MPa) have been studied. The effect of volume fraction of components on sintering process and microstructure has been investigated by Scanning Electron Microscopy of fracture surfaces of samples. The amount and the type of porosity and relative density of samples have also been determined. Results show that the density of samples decreases inversely with the amount of B4C. Also, the type of porosity changes from closed to open in high B4C volume fractions. SEM micrographs show that the sintering process is controlled by moss-like ZrO2 transient phases formed during the heating process.

플라즈마 질화처리에 따른 AISI 403 스테인리스강의 고상입자 침식마모거동

This study investigated the effects of plasma nitriding on the erosion behavior of AISI 403 stainless steel solid state particles at ambient temperature and 620 °C using Fe3O4 erodent particles at impact angles of 15-90 . The plasma nitriding formed a thick hardened layer which had a high microhardness of 1210 ± 15 Hv. At ambient temperature, AISI 403 suffered from severe erosion damage at low impact angles and exhibited ductile erosive behavior, while the nitrided layer experienced no significant damage at any impact angles. For AISI 403, the erosion rates at 620 °C were ~2 times higher than those obtained at ambient temperature. When eroded at 620 °C, the nitrided layer exhibited a ductile erosive manner, with a maximum erosion rate occurring at a low impact angle of 30 . The results from high temperature hardness measurement and the observation of the eroded surface are discussed to explain the high-temperature erosion behavior of the nitrided AISI 403 stainless steel. †(Received October 18, 2013)

Preparation and application of copolymer modified with the palygorskite as inhibitor for calcium carbonate scale

The scale inhibitor copolymer modified with palygorskite was prepared from maleic anhydride, styrene sulfonic sodium and palygorskite. The conditions of preparing scale inhibitor were optimized. The structure and morphology of the copolymer were characterized by FT-IR, SEM and XRD. Using the static experiment method, the influences of copolymer concentration, temperature, time, and Ca2+ concentration of the system on the inhibition efficiency were investigated. The experimental results showed that the scale inhibitor copolymer modified with palygorskite had an excellent efficiency of scale inhibition, and nearly 98.97% of scale inhibition efficiency for CaCO3 was obtained. The prepared scale inhibitor could be used in the system of high temperature and high hardness water.

Variation of carbon concentration in proeutectoid ferrite during austenitization in hypoeutectoid steel

The variation of the C concentration in proeutectoid ferrite (αPF) during austenitization in hypoeutectoid steels was quantitatively investigated using the massive transformation start temperature (Tm) of αPF to austenite (γ) measured by high-temperature confocal laser scanning microscopy and hardness of αPF. The C concentration in αPF at Tm in hypoeutectoid steels increased with increasing total C concentration up to approximately 0.2wt.% during heating. The hardness of αPF with isothermal holding time at 775°C in S20C steel revealed C enrichment in αPF at the early stage of isothermal holding and its reduction with further holding. These results explain the redistribution of the C in αPF during austenitization as follows: free C atoms released from cementite during pearlite decomposition diffuse excessively into neighboring αPF as well as pearlitic ferrite. The supersaturated C concentration in αPF is reduced during the long-range diffusive transformation of αPF to γ. However, some of the excess C atoms still remain in αPF until αPF starts to massively transform to γ.