440C Stainless Steel Research Articles

Rigorous model-based uncertainty quantification with application to terminal ballistics—Part II. Systems with uncontrollable inputs and large scatter

This Part II of this series is concerned with establishing the feasibility of an extended data-on-demand (XDoD) uncertainty quantification (UQ) protocol based on concentration-of-measure inequalities and martingale theory. Specific aims are to establish the feasibility of the protocol and its basic properties, including the tightness of the predictions afforded by the protocol. The assessment is based on an application to terminal ballistics and a specific system configuration consisting of 6061-T6 aluminum plates struck by spherical 440c stainless steel projectiles at ballistic impact speeds in the range of 2.4–2.8km/s. The system's inputs are the plate thickness, plate obliquity and impact velocity. The perforation area is chosen as the sole performance measure of the system. The objective of the UQ analysis is to certify the lethality of the projectile, i.e., that the projectile perforates the plate with high probability over a prespecified range of impact velocities, plate thicknesses and plate obliquities. All tests were conducted at Caltech's Small Particle Hypervelocity Range (SPHIR), which houses a two-stage gas gun. A feature of this facility is that the impact velocity, while amenable to precise measurement, cannot be controlled precisely but varies randomly according to a known probability density function. In addition, due to a competition between petalling and plugging mechanisms for the material system under consideration, the measured perforation area exhibits considerable scatter. The analysis establishes the feasibility of the XDoD UQ protocol as a rigorous yet practical approach for model-based certification of complex systems characterized by uncontrollable inputs and noisy experimental data.

Effect of reinforcement morphology on high-speed sliding friction and wear of PEEK polymers

Abstract Advanced engineering polymeric materials such as poly-ether-ether-ketone (PEEK) are increasingly being used for challenging tribological application. Some of these applications involve severe contact conditions. Reinforcing materials such as carbon fiber are often incorporated into polymeric materials to improve mechanical and thermal properties. In the present study the friction and wear behaviour was evaluated for various PEEK disc materials in high-speed (up to 65 m/s) sliding contact with 440C stainless steel balls using a 3 ball-on-flat contact configuration. Two of the tested PEEK materials were reinforced, one with long woven fiber and one with short, randomly oriented fibers, in addition to a base PEEK with no reinforcement. In general, at high sliding speeds, the friction and wear behaviour is related to the morphology of the reinforcement through the mechanisms of polymer transfer layer formation, abrasive wear rate of the steel ball, and thermal management of frictional heat generation. Under the current test conditions it is shown that the material with long woven reinforcement exhibits the lowest wear rate and lowest friction at high sliding speeds.

Metallurgical Analysis of Ball Bearing Seized During Operation

440C stainless steel of martensitic grade is being extensively used for bearing application because of its high wear and corrosion resistance. This alloy steel with 1 wt.% C along with 17 wt.% Cr, 1 wt.% Mn and up to 0.75 wt.% Mo has a number of primary carbides, which provide high hardness and good wear resistance. Owing to its unique performance characteristic, this steel finds a number of applications in space program. One such application is bearing used in booster pump assembly of propulsion system. During one of the ground tests of propulsion system, booster pump bearing seized operation after performing its partial intended function. The bearing was removed from the assembly and cut open. The ball and outer caging were analyzed using metallographic techniques and compared with another bearing taken from the fresh stock. Study indicated that ball as well as outer caging experienced exposure to high temperature and resulted in phase transformation. This article highlights the details of investigations carried out.

Fretting wear characteristics of cold gas-dynamic sprayed aluminum alloys

Process selection for repair of mechanical components due to wear and corrosion, e.g. damage of aluminum casting housings of fuel injection systems, is based on cost and response time factors, provided that the mechanical performance is maintained within acceptable limits. One of the promising and emerging repair technologies is Cold Gas-Dynamic Spray (CGDS) coating, where a high-pressure gas propels fine powder particles to very high velocities to produce surface coating. It is essential to identify the optimum process conditions and powder composition to produce repaired surfaces with tribological properties close to those of the originally manufactured part (without coating). The objective of this work is to compare the dynamic friction and fretting wear properties of the repaired surfaces using various types of coating composition and spraying techniques. Eight types of CGDS coatings, applied to AMS 4260 aluminum specimens, were fretted against 440C stainless steel specimens at low and high nominal loads to assess their fretting wear resistance, dynamic friction properties and damping capacity. The optimum coating composition and process conditions were identified. In comparison to the uncoated specimen, this optimum coating offered tribological characteristics close to the uncoated material and even better dynamic friction properties.

Is Ultra-Low Friction Needed to Prevent Wear of Diamond-Like Carbon (DLC)? An Alcohol Vapor Lubrication Study for Stainless Steel/DLC Interface

The effects of n-pentanol vapor on friction and wear of hydrogenated diamond-like carbon (DLC) films during sliding against a 440C stainless steel (SS) ball were investigated with a reciprocating pin-on-disc tribometer. Under dry sliding conditions, the friction coefficient is initially high (>0.2) for a so-called run-in period and then gradually subsequently decreases to an ultra-low value (<0.025). During the run-in period, a carbon transfer film is formed on the SS ball side, which seems to be the key for the ultra-low friction behavior. In n-pentanol vapor environments, the friction coefficient remained nearly constant at ~0.15 throughout the entire test cycles without any noticeable run-in period. Although the friction coefficient is high, there is no visible wear on rubbing surfaces when examined by optical microscopy, and the transfer film forming tendency on the SS ball side was much reduced. In humid environments, the wear prevention effect is not observed and transfer films do form on the ball side. These results imply that the n-pentanol layer adsorbed on DLC film from the vapor phase provides a molecularly thin lubrication layer which can prevent the substrate from wear.

Effects of Microstructural Evolution and Mechanical Properties on 440C-TiC Composite Steel by HIP Treatment

The aim of this paper is to investigate the effects of HIP treatment on 440C-TiC composite steel. In this study, AISI 440C stainless steel powders were added with different amounts of TiC powders (25, 33 and 40 wt%), the composite materials were sintered at 1473 K, 1573 K, and 1673 K, followed by different pressures of HIP and HIP plus heat treatment. HIP treatments were used 120 and 150 MPa at 1523 K 1 hour. Experimental results showed that the microstructure of matrix had small needle structures after HIP treatment, which were effective in improving the hardness and strength. Furthermore 440C-TiC composite steels which were added with 25wt% TiC powder after 1673 K sintered and high pressure HIP treatments, TiC powders were uniformly dispersed in the high chromium stainless steel matrix were observed and consequently possessed the higher hardness (HRA 85) and highest TRS (1213 MPa).

Control of lubricant transport by a CrN diffusion barrier layer during high-temperature sliding of a CrN–Ag composite coating

CrN–Ag composite coatings, 2 and 5 μm thick and containing 22 at.% Ag solid lubricant, were grown on Si(001) and 440C stainless steel substrates by reactive co-sputtering at T s = 500 °C, and were covered with 200 nm thick pure CrN diffusion barrier cap layers. Annealing experiments at T a = 625 °C, followed by quantitative scanning electron microscopy, energy dispersive x-ray spectroscopy, and Auger depth profile analyses indicate considerable Ag transport to the top surface for a barrier layer deposited at a substrate floating potential of −30 V, but negligible Ag diffusion when deposited with a substrate bias potential of −150 V. This is attributed to ion-irradiation induced densification which makes the cap layer an effective diffusion barrier. High temperature tribological sliding tests of this coating system against alumina balls at T t = 550 °C indicate an initial friction coefficient μ = 0.43 ± 0.04 which decreases monotonically to 0.23 ± 0.03. This is attributed to the development of wear mediated openings in the barrier layer which allow Ag lubricant to diffuse to the sliding top surface. In contrast, pure CrN exhibits a constant μ = 0.41 ± 0.02 while CrN–Ag composite coatings without cap layer show a low transient μ = 0.16 ± 0.03, attributed to Ag transport to the surface, that however increases to μ = 0.39 ± 0.04 after ~ 6000 cycles as the Ag reservoir in the coating is depleted. That is, the dense CrN cap layer reduces the Ag lubricant flow rate and therefore prolongs the time when the coating provides effective lubrication. This results in a cumulative wear rate over 10,000 cycles of 3.1 × 10 −6 mm 3/Nm, which is 3.3 × lower than without diffusion barrier layer.

Fretting Wear Study on Micro-Arc Oxidation TiO2 Coating on TC4 Titanium Alloys in Simulated Body Fluid

Tribological properties of TiO2 coatings synthesized by micro-arc oxidation (MAO) on the surface of TC4 titanium alloys were investigated at the fretting contact against 440C stainless steel in simulated body fluid (SBF). Fretting experiments were carried out by ball-on-flat contact at various loads for 1 h, with an amplitude of 100 μm and a frequency of 5 Hz. Results show that MAO TiO2 coatings presented good tribological properties with lower friction coefficient in SBF. Less wear volume was observed for MAO TiO2 coatings compared with that for TC4 alloy. At lower load, the wear mechanism of MAO TiO2 coatings was dominated to abrasive wear. With an increase of normal load, however, fretting corrosion increased due to chemical reactions with SBF, and therefore, fretting fatigue coexisting with abrasive wear became the predominant mode.

Powder injection molding 440C stainless steel

In this work, the processing steps for producing 440C stainless steel parts by means of powder injection molding technique were investigated. The molded specimens were debinded by solvent debinding followed by thermal debinding methods and were sintered under vacuum atmosphere. Effective densification took place in the temperature range 1,230–1,240°C in the sintering. After heat treatment, specimens sintered at 1,240°C for 30 min had the tensile strength of 876.3 MPa, the hardness of 57.7 HRC. Pitting mainly occurred in injection molding 440C stainless steel specimens in NaCl solution. The content of carbon has serious effect on the shape retention. Some methods, such as preventing from oxidation, are presented to avoid the as-sintered specimens from deformation.

Study on the Characteristics of Transferred Lubricating Thin Films on Ceramic Surfaces Generated in Liquid Nitrogen

Ceramic bearings working in liquid nitrogen are mainly lubricated by thin films transferred from the polytetrafluoroethylene (PTFE) based composite retainers. The thin films on silicon nitride ball surfaces are generated by the friction and interaction among the composite retainer, the balls, and the AISI 440C stainless steel rings. The characteristics of transfer lubricating films on silicon nitride ball surfaces generated during operation in liquid nitrogen at 2.4 and 2.8 GPa were analyzed. The distribution of thin films on the silicon nitride ball surfaces was observed by an optical microscope. The profile of transferred thin films was measured using an atomic force microscope (AFM). The component and structure of transferred thin films were detected by X-ray photoelectron spectroscopy (XPS) and Raman spectrometry. The results show that the distribution of transferred thin films on the silicon nitride ball surfaces is discontinuous and its thickness is about one micrometer. The upper layer of the transfer films, about 100 nm thick, degrades under a heavy load, generating metal fluoride. The bonding strength between the degradation layer and its basis is very weak.

A Microfabricated Spiral-Groove Turbopump Supported on Microball Bearings

The development of a microfabricated turbopump that is capable of delivering liquid fuel with the flow rates and pressures required for portable power generation is reported. The device is composed of a spiral-groove viscous pump driven by a radial in-flow microturbine and supported using a newly developed encapsulated microball bearing. A planar-contact bearing raceway is employed using 285-?m -diameter 440C stainless steel microballs. A modification to the raceway geometry, as compared to previous designs, has enabled repeatable operation of the microturbine at speeds up to 87 000 r/min, showing negligible variations in performance for over 6 h and 3.8 million revolutions. Pumping has been demonstrated with water as the working fluid for flow rates of 10-80 mL/h and pressures rises of up to 8.2 kPa. This is the first application to incorporate an encapsulated microball bearing support mechanism, to achieve rotational speeds in excess of 50 000 r/min using a contact bearing, and to demonstrate reliable operation of more than 1 million revolutions.

Corrosion wear behaviors of micro-arc oxidation coating of Al 2O 3 on 2024Al in different aqueous environments at fretting contact

The fretting wear behavior of micro-arc oxidation (MAO) coating of Al 2O 3 on an aluminum alloy 2024Al flat against a 440C stainless steel ball was investigated in artificial rainwater, artificial seawater and distilled water by using a ball-on-flat configuration with 300 μm amplitude at room temperature for 1 h. The morphology of the wear scars were observed and analyzed using scanning electron microscopy; the 3D-morphology and wear volume-loss were determined using a non-contact optical profilometer. Potentiodynamic anodic polarization was used to measure the corrosion behavior of the MAO coating before and after the corrosion wear test. The influences of the load, frequency and aqueous medium on the friction coefficient and wear volume-loss of the coatings were also analyzed. Results show that the friction coefficient decreases generally with an increase of the frequency in the three aqueous solutions; whereas it presents different variation trends as the load increased. In addition, aqueous environment does significantly influence the friction coefficient, the friction coefficient was the largest when fretting occurred in distilled water, smaller when fretting occurred in rainwater, and the smallest when fretting occurred in seawater. Particularly the remarkable antifriction effect of the seawater is of note. The wear-loss of the MAO coating in the distilled water is the largest at low frequency; however, it increases rapidly in rainwater and seawater at high frequency due to the corrosion effect of Cl − ion as well as its accelerating effect to the wear process, and results in larger wear-loss than that in distilled water, which implies a positive synergism between corrosion and wear.

CrN–Ag nanocomposite coatings: Tribology at room temperature and during a temperature ramp

5 µm thick CrN–Ag composite layers with 22 at.% Ag were deposited by reactive magnetron co-sputtering on 440C stainless steel substrates. Increasing the growth temperature from T s = 500 to 600 to 700 °C leads to Ag segregation within the CrN matrix and the formation of embedded lamellar Ag aggregates with increasing size, < 10 5, 9 × 10 6, and 7 × 10 7 nm 3, respectively. Ball-on-disk tests against 100Cr6 steel, followed by optical profilometry and energy dispersive spectroscopy, indicate that the Ag grains for T s = 500 °C are too small to facilitate an effective lubricious surface layer, resulting in a friction coefficient μ = 0.58 and a composite coating wear rate of 3.8 × 10 − 6 mm 3/Nm that are nearly identical to those measured for pure CrN with μ = 0.64 and 3.6 × 10 − 6 mm 3/Nm. The T s = 600 °C coating exhibits a Ag concentration which is 15% higher within than outside the wear track, and acts as a lubricious layer that reduces μ to 0.47 and yields a 16× and 2.4× lower wear rate for coating and counterface, respectively. T s = 700 °C leads to a dramatic increase in surface roughness and an associated increase in friction, μ = 0.85, and wear, 9.9 × 10 − 6 mm 3/Nm. Replacing the steel counterface with an alumina ball results in the lowest μ = 0.50 for T s = 500 °C, attributed to the presence of Ag and the relatively low hardness of 16.5 GPa for this particular coating. In contrast, friction and wear increase dramatically for T s = 600 °C, which is attributed to a breakdown of the lubricious Ag layer by the harder counterface. The transient friction coefficient μ t during experiments with continuously increasing testing temperature T t = 25–700 °C initially decreases for all samples, attributed to drying of the environment and an effective softening of both coating and counterface. For the T s = 500 °C coating, a temperature activated solid lubricant transport yields a lubricious Ag surface layer and a very low μ t = 0.05 at T t ~ 500 °C. All coatings exhibit an increasing μ t for T t > 500 °C, which is attributed to oxidative degradation.

Characterization of Diamond-Like Carbon Coating on 16Cr-1C Martensitic Stainless Steels

The 16Cr-1C martensitic stainless steel can provide the higher hardness and better wear resistance for 440C steel. The microstructure of DLC coatings were observed by optical microscope and field-emission scanning electron microscope (FE-SEM). The compositional depth profile of DLC films were measured by field-emission Auger electron spectroscopy (Fe-AES). In addition, the micro-hardness and elastic modulus of DLC films were measured by nano-indentation tests. Experimental results show that the total thickness of coating was in the range of 600nm~1100nm. This coating was included of Ti/TiC transition layer and DLC layer. The Ti/TiC transition layer was grown on the 440C stainless steel substrate, and the upper layer was DLC layer. This layer structure was confirmed by the FE-AES analysis. The micro-hardness of DLC coating was measured in the range of 24.2GPa~26.0GPa, and the elastic modulus was measured in the range of 264GPa~313GPa in the nanoindentation test. The nanoscratch results show that DLC films have lower friction coefficients than 440C substrate.

The effects of sliding velocity and sliding time on nanocrystalline tribolayer development and properties in copper

The growth of the nanocrystalline tribolayer produced in oxygen free high conductivity copper after sliding against 440C stainless steel was studied. Tests were conducted on a pin-on-disk tribometer at sliding velocities of 0.05 and 1.0 m/s and sliding times of 0.1 to 10,000 s. Subsurface deformation and the growth of the tribolayer as a function of time were studied with the use of transmission electron microscopy and ion induced secondary electron microscopy. A continuous nanocrystalline tribolayer was produced after as little as 10 s of sliding at both sliding velocities. The tribolayer produced by sliding at 0.05 m/s continued to grow at sliding times up to 10,000 s and developed texture. Dynamic recrystallization of the tribolayer at a sliding velocity of 1.0 m/s inhibited the growth of a continuous nanocrystalline tribolayer.

Corrosion wear behaviors of 2024Al in artificial rainwater and seawater at fretting contact

The fretting wear behaviors of an aluminum alloy 2024Al flat specimen against a 440C stainless steel counter ball specimen were evaluated in distilled water, artificial seawater and rainwater by using a ball-on-flat configuration with 300 μm amplitude at room temperature for 1 h. Potentiodynamic anodic polarization was used to measure the corrosion behaviors of 2024Al before and after the corrosion wear test. The worn surfaces of the specimens were observed using scanning electron microscopy (SEM). The valence of the elements on the wear scars was detected by X-ray photoelectron spectroscopy (XPS). The 3D-morphology and wear volume-loss were determined using a non-contact optical profilometer. The influences of the frequency and aqueous mediums on the friction coefficient and wear loss were analyzed. Results show that the friction coefficient decreases generally with the frequency increasing in the three aqueous solutions. The friction coefficient decreases 21.47% in rainwater and 47% in seawater compared with that in distilled water. This indicates the considerable influence of aqueous solutions on the friction coefficient due to the lubricative film formed on the 2024Al specimens. However, the wear loss in both the corrosive solutions is always larger than that in distilled water due to the erosion effect of chlorine ions on the wear scar. Wear loss increased in distilled water, increased more in rainwater, and increased even more in seawater; this demonstrates a positive synergism between corrosion and wear. The contribution of synergism (Δ V) to total wear loss ( V) of 2024Al reveals that the synergism is worse in seawater than in rainwater. The wear mechanism of 2024Al is dominating abrasion wear in rainwater, whereas it becomes corrosion fatigue in seawater.

Fretting Tribology of Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;/Cu Composite Prepared by Powder Metallurgy

The nano-Al2O3 reinforced copper matrix composite was prepared by powder metallurgy technique and the fretting test against 440C stainless steel was performed at room temperature by using the ball-on–flat configuration with 300μm amplitude at various normal loads in the range of 0.1N to 1N. The influences of load and proportion of Al2O3 on the friction coefficient and volume wear -loss were investigated. Results showed that the volume wear-loss decreased firstly and then increased as the proportion of Al2O3 increased from 0.5% to 4%, and the minimum proportion was about 2%, in which the electrical conductivity can reach up to 81% according to International Annealed Copper Standard (IACS). The friction coefficient of the copper will slightly increases as the load increased. However, in the case of composites, it increased firstly then decreased. The volume wear-loss of the composite is always lower than that of copper, giving the highest relative wear-ability of 1.55, which indicated a higher wear resistance. The wear mechanism of copper is adhesive wear, whereas it becomes oxidation wear in composites.

Effect of counterparts on the friction and wear behavior of polyelectrolyte multilayers

Polyelectrolyte multilayers (PEMs) were prepared on Si substrates by alternative deposition of poly(sodium 4-styrenesulfonate) (PSS) as polyanion and poly (diallyldimethylammonium chloride) (PDDA) as polycation. The PEM film was characterized by means of ultraviolet-visible light absorption spectrometry and atomic force microscopy. The friction and wear behavior of the polymer film sliding against brass, 440C stainless steel, Si 3N 4 and WC balls was evaluated on a microtribometer. It was found that the multilayer film was uniform and compact, and it registered a lowered friction coefficient and extended antiwear life while sliding against soft counterparts, in particular, a brass ball. This could be because the polymeric transfer film had an enhanced adhesion on the soft metallic counterpart in the presence of inter-transferred metallic debris. Contrary to the above, the PEM film had a higher friction coefficient and shorter antiwear life while sliding against Si 3N 4 and WC balls, possibly owing to a higher shearing stress in the presence of stiff and hardly deformable hard counterparts. In other words, the polymeric transfer film on the hard couterparts, if any, would be easily scaled off, leading to decreased antiwear life. Moreover, the differences in the friction and wear behavior of the PEM film sliding against different counterparts were closely related to the differences in the chemical and crystallographic structure of the counterparts (ceramics Si 3N 4 and WC, and metals brass and stainless steel).

Finite Element Analysis of Multilayered and Functionally Gradient Tribological Coatings with Measured Material Properties

A model has been developed to study the stress distribution in Ti1 − xCx multilayered functionally gradient (FG) coatings, with a top coating of diamond-like carbon (DLC), on 440C stainless steel substrates. Using the finite element method, these gradient coatings were assumed as a series of perfectly bonded layers with unique material properties and layer thickness. In addition, a matrix of nanoindentation experiments were performed to measure material properties of each Ti1 − xCx layer on separate coating blocks. The yield strength of the coating materials was then determined by coupling the finite element analysis model in connection with the nanoindentation technique. Once developed, this model was used to examine the threshold of plasticity and identify the plastic deformation zone inside the multilayered coatings and substrate. This work shows how the multilayered FG Ti/TiC/DLC coating system improves the coating integrity under heavy loading conditions.

Preparation and characterization of polyelectrolyte multilayer films containing in-situ synthesized nanoparticles of Cu(OH) 2

Copper ions-loaded polyelectrolyte multilayer films (PEMs) of poly(acrylic acid), coded as PAA, and poly(diallyldimethylammonium chloride), coded as PDDA, were constructed on silicon substrate via layer-by-layer (LBL) self-assembly, using CuCl 2 blended in the electrolyte solution as the source of Cu 2+. Cu(OH) 2 nanoparticles were then in-situ synthesized in the multilayer films by immersion of the copper ions-loaded PEMs into 0.1 M NaOH solution. The Cu 2+-loaded PAA/PDDA multilayer films and those doped with in-situ Cu(OH) 2 nanoparticles were characterized by means of ultraviolet–visible light (UV–vis) absorption spectrometry, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The friction and wear behaviors of the multilayer films sliding against 440C stainless steel counterparts were evaluated using a UMT-2 multifunctional micro tribometer. Results indicate that the Cu 2+-loaded PAA/PDDA multilayers with a bilayer number of 2–8 show similar UV–vis absorbance features, and no noticeable accumulation in the amount of Cu 2+ occurs during the fabrication of the multilayers, possibly owing to a weak bonding between Cu 2+ and –COO −. The blue-shift of the absorption peak of –COO −–Cu 2+ band, observed for PAA/PDDA multiplayer films, becomes more obvious after being doped with in-situ Cu(OH) 2 nanoparticles. The final Cu(OH) 2 nanoparticles-doped PAA/PDDA multilayer films have excellent friction-reducing and antiwear abilities, possibly owing to the modification and refining of their morphology and microstructure by the in-situ doped Cu(OH) 2 nanoparticles. The present approach could be extended to incorporate nanoparticles of other types of metal ions into the final PEMs to realize multifunctionalization.