Hot Hardness Research Articles

Effect of C Content on High Temperature Erosive Wear Characteristics of Fe-Based V Containing Multi-Component Cast Steel with Ni

Hot hardness and oxidation property of target material influences greatly on the erosion behavior at elevated temperature. The correlation between hot hardness and oxidation property of multi component white cast irons and its erosion resistance were investigated, and try to estimate the high temperature erosion behavior in the study. Nine kinds of multi component white cast iron and cast steel were used in this study. Specimen were machined into a flat plate with dimension of 50×50×10 mm. High temperature erosion test machine was used to investigate the erosive wear property of experimental materials at 1173K. Alumina grits (average diameter: 1.16 mm, hardness: 1250 HV1) which were used as impact particles were heated to 1073K and shoot on the heated specimen by hot air at the velocity of 100 m/s. The total particle loading was 2 kg. In order to clarify the correlation of hot hardness, oxidation property and the erosion resistance of specimens, hot hardness test was carried out specimens, to estimate erosion damage caused by solid particle. Hot hardness of specimens showed a value comparable to 200～250HV1. Result of erosion and oxidation tests, erosion rate and amount of oxidation of the specimen were suppressed by Ni addition. It suggested that the more amount of Ni contents, the lower the erosion rate and the less the amount of oxidation.

Exploring the influence of constitutive models and associated parameters for the orthogonal machining of Ti6Al4V

Ti6Al4V is known as difficult-to-cut material due to its inherent properties such as high hot hardness, low thermal conductivity and high chemical reactivity. Though, Ti6Al4V is utilized by industrial sectors such as aeronautics, energy generation, petrochemical and bio-medical etc. For the metal cutting community, competent and cost-effective machining of Ti6Al4V is a challenging task. To optimize cost and machining performance for the machining of Ti6Al4V, finite element based cutting simulation can be a very useful tool. The aim of this paper is to develop a finite element machining model for the simulation of Ti6Al4V machining process. The study incorporates material constitutive models namely Power Law (PL) and Johnson – Cook (JC) material models to mimic the mechanical behaviour of Ti6Al4V. The study investigates cutting temperatures, cutting forces, stresses, and plastic strains with respect to different PL and JC material models with associated parameters. In addition, the numerical study also integrates different cutting tool rake angles in the machining simulations. The simulated results will be beneficial to draw conclusions for improving the overall machining performance of Ti6Al4V.

Study of dry sliding wear characteristics of stellite 6B versus AISI M2 steel at various sliding velocities

The wear performance of Stellite 6B versus AISI M2 steel in dry sliding at various sliding velocities (from 0.95 to 4.71 m/s) were systematically studied by pin-on-disc wear test and analysis of debris, tribo-layers and worn surfaces of both pin and disc. The mechanical performance of pin and disc were also studied by hot hardness test. The results showed that Stellite 6B underwent a severe-to-mild wear transition with the increase of sliding velocity in the Stellite 6B alloy/steel tribo-system. The temperature at worn surface increased with the increase of velocity and load, leading to the oxidation of the worn surface and the variation of mechanical strength of pin and disc. It was the surface state rather than the variation of the mechanical strength that impacted the wear transition. The critical transition sliding velocity for the Stellite 6B alloys was 2.51 m/s, which divided the sliding velocities into two regions. When the velocity was among 0.95–2.51 m/s, the wear mechanism turn from abrasive and delamination wear to adhesive wear gradually, resulting in the decrease of wear rate. While in the region that the sliding velocity was above 2.51 m/s, oxidative wear prevailed and the wear rate decreased due to the formation of mechanically mixed layer (MML).

Potentials of niobium carbide (NbC) as cutting tools and for wear protection

Apart by vacancies, the different pseudo-cubic phases NbC, Nb4C3 and Nb6C5, can accommodate any stoichiometry of NbCx (0.75 ≤ x ≤ 1.0) in the binary phase diagram and enable a large process window. Properties, like micro-hardness, hot hardness, sliding wear resistance, elastic modulus and toughness can be tailored by the C/Nb ratio, the addition of secondary carbides and the type of binder. SPS sintered and cobalt bonded (NbC0.88-12Co SPS). NbC and Nb2O5 have so far no REACH classifications related to human toxicology and are not listed as substances of very high concern contrary to Co3O4. The NiMo-bonded stoichiometric NbC1.0 grades enable the substitution of cobalt by nickel, SPS by conventional sintering and NbC0.88 by NbC1.0 in view of functional properties. Nickel bonded NbC grades have improved toughness versus cobalt bonded NbC grades, but loosed in hardness. NiMo and NiMo2C bonded NbC1.0 grades in combination with secondary carbides compensated the loss in hardness while keeping the toughness. The tool lifes of uncoated NbC1.0-12Ni4Mo4VC and NbC0.88-12Co under dry turning of 42CrMo4 and C45E were between +30% to +200% higher and up compared to WC-6Co (extra fine grain). Niobium is today largely available as resource. NbC grades displayed lower dry sliding friction over WC grades. The softer Ni- and NiMo-bonded NbC1.0-grades have a higher dry abrasive wear resistance (ASTM G65), even with lower toughnesses, as the tougher WC-Co grades.

High-Temperature Mechanical Properties of the P/M Extruded Mg-SiCp Composites

In the present study, pure magnesium reinforced with 0, 5, 10 and 15 vol.% SiC particulates was successfully prepared by powder metallurgy technique before being hot extruded. The average 14 μm grain size of the composite specimens remained almost unchanged after addition of SiC particles, while their dimensional stability was improved because of the reduction in the coefficient of thermal expansion (CTE) from 28.6 × 10−6 K−1 in pure Mg to 27.3, 25.3 and 23.4 × 10−6 K−1 in the Mg-5% SiC, Mg-10% SiC and Mg-15% SiC composites, respectively. Mechanical properties of the specimens were investigated in the temperature range of 298-498 K, implementing shear punch testing and hot hardness techniques. Depending on the test temperature, addition of SiC particles to the pure Mg matrix increased shear yield stress and ultimate shear strength of the materials by 5-25 and 6-23 MPa, respectively. The shear strength improvement was mainly attributed to the CTE mismatch strengthening mechanism (9.5-25.5 MPa), and to a lesser extent (1-4.5 MPa), to the load transfer mechanism. Finally, using the modified Clyne model, the contribution of different strengthening mechanisms to the total shear strength improvement in the composites was evaluated.

Increased tool performance with niobium carbide based cutting materials in dry cylindrical turning

Niobium carbide (NbC) shows promising results as an alternative cutting tool material to tungsten carbide (WC) for turning of iron-based materials. Due to its hot hardness and low solubility of binderless NbC in solid chrome, nickel, cobalt, or iron, it presents excellent properties for cutting tool applications. These advantages result in a reduced tendency to adhesive and diffusion wear, which affects cutting tool lifetime and process stability. In order to investigate a possible substitution of the conventional substrate material tungsten carbide, the BAM Federal Institute for Materials Research and Testing and the Institute for Machine Tools and Factory Management (IWF) of the Technische Universität Berlin analyze the suitability of NbC for the use as a cutting tool in turning processes. Two different straight NbC materials are included in the machining trials prepared by Katholieke Universiteit Leuven, Belgium each differing in chemical composition and mechanical properties. A cobalt (Co) bonded niobium carbide defined as NbC0.88-12Co, a nickel (Ni) bonded NbC with the specification (NbC1.0-10TiC)-6Ni7.5VC and a commercially available cermet with a niobium content of wt.-%NbC = 25 % are selected and compared to submicron grain WC-6Co tool material. Carbon steel C45E and gear steel 42CrMo4+QT are chosen as workpiece materials of different representative technological applications for dry external cylindrical turning tests. A variation of cutting speed is carried out to show the impact of higher thermomechanical load during machining. The results evaluate the cutting performance of NbC compared to WC regarding material removal VW and crater wear KT. In contrast to WC tools NbC cutting tools show constant material removal VW at increased cutting speed vc combined with a higher process reliability.

Investigation on the grinding characteristics of binderless nanocrystalline cubic boron nitride (BNNC) as cutting material for the machining of hardened steels and superalloys

The direct synthesis of a binderless nanocrystalline cubic boron nitride (BNNC) from hexagonal boron nitride (hBN) has been developed by using a high-pressure / high-temperature process (HP/HT) with temperatures from 1400 °C - 2200 °C and pressures from 10 GPa - 20 GPa, the resulting BNNC compacts have a high hardness of more than 50 GPa as determined by Knoop-Indentation. A phase content of up to 97 % cBN could be determined by X-ray diffraction (XRD). The average crystallite size of the material is smaller than 100 nm and therefore significantly smaller than the crystallite size of conventional polycrystalline cubic boron nitride (PcBN) cutting materials. Compared to established PcBN cutting materials, the BNNC has an increased hardness and hot hardness and improved temperature stability. Utilization BNNC-based tools with defined cutting edge could provide an excellent alternative for the enhancement of the process limits for the machining of hardened steels and superalloys. This conference contribution will present the latest developments and challenges in the HP/HT direct synthesis of binderless nanocrystalline boron nitride (BNNC) as well as the investigation of its grinding characteristics for the application as cutting insert.

Technics Research on Polycrystalline Cubic Boron Nitride Cutting Tools Dry Turning Ti-6AL-4V Alloy Based on Orthogonal Experimental Design

Ti-6Al-4V components are the most widely used titanium alloy products not only in the aerospace industry, but also for bio-medical applications. The machine-ability of titanium alloys is impaired by their high temperature chemical reactivity, low thermal conductivity and low modulus of elasticity. Polycrystalline cubic boron nitride represents a substitute tool material for turning titanium alloys due to its high hardness, wear resistance, thermal stability and hot red hardness. For determination of suitable cutting parameters in dry turning Ti-6AL-4V alloy by Polycrystalline cubic boron nitride cutting tools, the samples, 300mm in length and 100mm in diameter, were dry machined in a lathe. The turning suitable parameters, such as cutting speed, feed rate and cut depth were determined according to workpieces surface roughness and tools flank wear based on orthogonal experimental design. The experiment showed that the cutting speed in the range of 160~180 m/min, the feed rate is 0.15 mm/rev and the depth of cut is 0.20mm, ideal workpiece surface roughness and little cutting tools flank wear can be obtained.

Technics Research on Polycrystalline Cubic Boron Nitride Cutting Tools Dry Turning Ti-6AL-4V Alloy Based on Orthogonal Experimental Design

Ti-6Al-4V components are the most widely used titanium alloy products not only in the aerospace industry, but also for bio-medical applications. The machine-ability of titanium alloys is impaired by their high temperature chemical reactivity, low thermal conductivity and low modulus of elasticity. Polycrystalline cubic boron nitride represents a substitute tool material for turning titanium alloys due to its high hardness, wear resistance, thermal stability and hot red hardness. For determination of suitable cutting parameters in dry turning Ti-6AL-4V alloy by Polycrystalline cubic boron nitride cutting tools, the samples, 300mm in length and 100mm in diameter, were dry machined in a lathe. The turning suitable parameters, such as cutting speed, feed rate and cut depth were determined according to workpieces surface roughness and tools flank wear based on orthogonal experimental design. The experiment showed that the cutting speed in the range of 160~180 m/min, the feed rate is 0.15 mm/rev and the depth of cut is 0.20mm, ideal workpiece surface roughness and little cutting tools flank wear can be obtained.

Experimental and PFEM-simulations of residual stresses from turning tests of a cylindrical Ti-6Al-4V shaft

Alloy Ti-6Al-4V is a frequently used material in aero space applications due the high strength and low weight. This material is however often considered as a difficult to machine alloy due to several material properties such as the inherent characteristics of high hot hardness and strength which is causing an increased deformation of the cutting tool during machining. The thermal properties also cause a low thermal diffusion from locally high temperatures in the cutting zone that allows for reaction to the tool material resulting in increased tool wear.Predicting the behavior of machining of this alloy is therefore essential when selecting machining tools or machining strategies. If the surface integrity is predicted, the influence of different machining parameters could be studied using Particle Finite Element (PFEM)-simulations. In this investigation the influence from cutting speed and feed during turning on the residual stresses has been measured using x-ray diffraction and compared to PFEM-simulations.The results showed that cutting speed and feed have great impact on the residual stress state. The measured cutting force showed a strong correlation especially to the cutting feed. The microstructure, observed in SEM, showed highly deformed grains at the surface from the impact of the turning operation and the full width half maximum from the XDR measurements distinguish a clear impact from different cutting speed and feed which differed most for the higher feed rate.The experimental measurements of the residual stresses and the PFEM simulations did however not correlate. The surface stresses as well as the sign of the residuals stresses differed which might be due to the material model used and the assumption of using a Coulomb friction model that might not represent the cutting conditions in the investigated case.

Multi Flank Chip Formation in Fir-Tree Broaching Inconel 718 with Cemented Carbide

In aero engines sector, the connection between turbine discs and blades is realized by profiled grooves. The standard process to manufacture these fir tree or dove tail slots is broaching with tools out of High Speed Steel (HSS). On the one hand HSS has a high toughness, on the other hand though only a low hot hardness compared to other cutting materials like cemented carbide. However, for the introduction of cemented carbide broaching tools a redesign of the tool micro and macro geometry is necessary. For this development of broaching tools made out of alternative cutting materials as cemented carbide, especially in the finishing sector, the chips are from major interest due to the multi-flank chip formation and the resulting mechanical tool load.In this work, the multi-flank chip formation in manufacturing internal radii with cemented carbide tools was investigated. High speed recordings and cutting force measurements were implemented to analyze the chip formation with regard to the typical chip formation phenomena like wrinkling and folding, which are already examined in gear manufacturing sector for gear hopping.

Evolution mechanisms of high temperature mechanical properties and microstructures of Al2O3/SiCw/TiCn nanocomposite materials

The addition of nanoparticles can greatly improve the mechanical properties of ceramic materials at room temperature, but the research on the toughening and strengthening effect of nanoparticles at high temperature is less reported. In this paper, the evolution law and evolution mechanisms of the mechanical properties including Vickers hardness, fracture toughness and flexural strength as well as elastic modulus of TiC nanoparticles dispersed Al2O3/SiCw ceramic materials (Al2O3/SiCw/TiCn) at high temperature (up to 1200 °C) were meticulously investigated compared with those of Al2O3/SiCw. The results showed that the Vickers hardness and fracture toughness of Al2O3/SiCw/TiCn were higher than those of Al2O3/SiCw ceramic materials at both room and elevated temperature. Although the flexural strength of the Al2O3/SiCw ceramic materials was improved by the addition of nanoparticles at room temperature, the intergranular fracture tended to occur along the refined matrix grains at high temperature, resulting in lower high temperature flexural strength of Al2O3/SiCw/TiCn composite. The Vickers hardness of both the two composites decreased with increasing temperature (20–1000 °C). At 1000 °C, the hot hardness of the composite with TiC nanoparticles addition was still maintained 68.4% of hardness at room temperature. The fracture toughness of the two composites decreased rapidly from 900 °C above but increased to a peak at 1200 °C. The addition of TiC nanoparticles played a positive role for improving the hot hardness and high temperature fracture toughness, but was not conducive to the high temperature flexural strength.

Prediction of cutting forces and vibration in titanium alloy milling using a toroidal cutter

Titanium alloys are frequently used when a high strength-to-weight ratio and good hot hardness, corrosion resistance, and fatigue properties are needed. One of the most widely used of these alloys is Ti-6Al-4V. However, titanium alloys with these characteristics generally have poor machinability and tend to cause the machine-tool-workpiece-fixture system to vibrate. In this work, a model for predicting the cutting forces in milling is adapted for milling with toroidal cutters, and the dynamic effects of machining are included in the model. The cutting constants are determined in milling experiments, and the dynamic parameters used in the vibration model are determined in modal tests. By including cutting vibration in the model, the vibration behavior during milling can be understood and the cutting forces in real milling processes can be better simulated.

Influence of Grinding Media Size and Sintering Time in the Processing of AISI D2 Tool Steel by High-Energy Milling

Tool steels are fundamental in the current production processes, as they are used in dies and molds, essential for the transformation of raw materials into the final product. The tool steels for cold work have a low hot hardness, so their use is limited to temperatures below 200° C. The D-X series of tool steels, high carbon and high chromium, have a high wear resistance and is much used in the manufacture of dies and molds. Despite the high hardness, these steels have a microstructure with coarse carbides, which affects the hardness of the material. An alternative to the processing tool steels is the high-energy milling and subsequent powder metallurgy, in order to refine the microstructure of the material. This work aimed to study the influence of the size of the grinding media in the refining of the microstructure of AISI D2 by high-energy milling and the microstructural changes with the increase in sintering temperature. The results indicated that grinding media of smaller diameters had higher efficiency in high-energy milling due to smaller mean particle size obtained by grinding and subsequent final reduction in the average size of carbides. The sintering time had a direct influence on the microstructure of the material, higher sintering times led to formation of lower bainite, after cooling from sintering temperature.

Microstructure and Wear Properties of Laser-Cladded cBN/Ti $$_{3}$$ 3 Al on Pure Titanium

In order to improve the tribological properties of titanium alloys at high temperature, the possibility of producing Ti\(_{3}\)Al intermetallic with the addition of ceramic (cBN) coatings on titanium substrate using laser technique cladding was investigated. cBN is generally known for its high hot hardness, wear resistance and chemical stability. Laser cladding is an emerging material processing technique which is an efficient and cost-effective technique for improving the surface properties of general metallic materials. This paper presents the effects of laser cladding on the phase combination, microstructure, hardness and wear resistance of titanium aluminide/cBN IMC composites at different variations in quantity of cBN in the composite. Optical microscopy, X-ray diffraction and scanning electron microscopy with EDX were used for characterising the microstructure of the coating. In addition, the composite coating was subjected to wear testing using the ball-on-disc, friction and wear apparatus. The XRD results revealed phases with small cBN, \(\hbox {Ti}_{2}\hbox {N}\) and \(\hbox {TiB}_{2}\) peaks in addition to the rich \(\gamma \)-Ti, \(\alpha 2\hbox {-Ti}_{3}\hbox {Al}\) and TiAl intermetallics phases in the coatings after cladding process, whereas the microstructure of the cBN cladded layer contained partially melted cBN grains evenly dispersed within the laths of alpha Widmanstatten phase in the form of dendrites, precipitate of \(\alpha _{2}\hbox {-Ti}_{3}\hbox {Al}\) and spherical-shaped pure titanium. The effect of the addition of cBN into \(\hbox {Ti}_{3}\hbox {Al}\) alloy at increasing weight percentages showed an improvement in the hardness and wear resistance of the coatings. The increase is attributed to reacted boron nitrides particles with titanium, being distributed uniformly in the intermetallic matrix.

Study of wear mechanisms at high temperature scratch testing

Wear of materials at high temperatures (HT) is a very challenging issue, implying many different mechanisms. Individual wear phenomena occurring during abrasive contact at HT can be investigated by scratch testing. To study the influence of temperature and load on scratch behaviour a novel scratch test was utilised, allowing for scratch investigations up to 1000°C. Three materials for HT usage were chosen for investigation: an austenitic steel, a cast steel with carbide network and a Ni-based material with carbide network. Test load was varied from 10 to 100N and temperature steps were room temperature, 500°C and 800°C. Additionally hot hardness tests were performed to measure the hardness-temperature dependency of the materials.The three materials show very diverging wear behaviour at the investigated temperatures. While at low temperatures the wear scars are relatively smooth, wear behaviour became instable with temperature induced material softening. Especially inhomogeneous materials show pronounced stick-slip phenomena at highest testing temperatures. To understand the wear behaviour in a greater detail, numerical simulations of the scratch process were undertaken using smooth particle hydrodynamics. First results show a good correlation with wear scars of the austenite and allow a deep insight in the stress distribution and deformation process during scratching.

Wear behavior of solid SiAlON milling tools during high speed milling of Inconel 718

Machining of Inconel 718 is a challenging process because of high hot strength and hardness, high reactivity with the tool materials and low thermal conductivity of Inconel 718 alloy. Although SiAlON ceramics in the form of indexable inserts are utilized successfully in turning and milling operations of Inconel 718, application of solid SiAlON milling cutters on high speed milling of superalloys is rare. In this study, SiAlON ceramics were manufactured in the form of solid milling cutters and tested in high speed milling of Inconel 718 in order to investigate the wear mechanisms during machining process. The wear based on the severe adhesion of the work-piece to the tool flank face and repeated formation and removal of an Al and Ti-rich diffusion layer was observed at the flank faces of the tools.

Fabrication and cutting performance of Ti(C,N)-based cermet tools used for machining of high-strength steels

Two kinds of Ti(C,N)-based cermet tools, namely TMWNC and TMWC, were fabricated for the machining of high-strength steels. This research investigated the cutting performances of both tools in terms of chip morphology, cutting force, cutting temperature, and tool wear and failure mechanisms. The results reveal that at the same cutting speed, the life of TMWC tool is longer than that of TMWNC tool with lower cutting force and higher cutting temperature than those of TMWNC tool. For TMWNC tool, at a lower cutting speed of 150m/min, the tool failure is caused by abrasive wear. And when the cutting speed increases further, the surface flaking and nose breakage occur due to the comprehensive effects of adhesive wear, abrasive wear and thermal-mechanical fatigue. While for TMWC tool, the tool wear is severe with chipping, as a result of adhesive wear and abrasive wear. The research has proven the application feasibility of TMWNC and TMWC tools in the machining of high-strength steels. The TMWNC tool with higher fracture toughness presents better edge chipping resistance, and the TMWC tool with higher hardness and hot hardness exhibits better resistance against breakage.

High temperature abrasion resistance of differently welded structural steels

Structural steels provide a broad spectrum of heat, creep and wear resistance at different microstructures and hardness levels. Two different steel grades were chosen for investigation and simulated repair welds with different parameters were performed, aiming on the influence of heat input during welding and the resulting microstructure on the high temperature abrasion resistance. The impact on the wear resistance and its temperature dependence was evaluated within a high temperature three-body abrasion test and a hot hardness test rig. Results indicate a strong dependence of present microstructural phases and hardness on the wear resistance entailed by different welding parameters. Optimised parameters and low energy input during welding leads to stable hot hardness progress and wear conditions for the investigated materials.

Comparison of machining performance of hole-sinking micro-EDM without and with ultrasonic vibration on titanium alloy

Titanium alloys are highly demanding in aerospace industries due to its high strength-to-weight ratio and high hot hardness, and termed as difficult-to-machine materials. Creating microholes of high accuracy in these materials is challenging task for manufacturing industries. Conventional twist drills are generally failed in the micromachining of Titanium alloys due to the low thermal conductivity of these alloys. In consideration of all these problems, authors used self-developed hole-sinking micro-EDM (HS-MEDM) setup without and with the assistance of ultrasonic vibration (UV) to create microholes in Titanium alloy (Ti-6Al-4V) workpiece. Comparative study regarding machining performance in terms of material removal rate (MRR), tool wear rate (TWR), hole taper (Ta) and overcut (OC) at different gap current, pulse on-time and pulse off-time has been reported without and with assistance of UV. It was found that HS-MEDM with UV is more advantageous in producing microholes with higher MRR, lower TWR, Ta and OC, and smoother surface.