Corrosion Resistance Applications Research Articles

Iron-Based Amorphous Metals: High-Performance Corrosion-Resistant Material Development

An overview of the High-Performance Corrosion-Resistant Materials (HPCRM) Program, which was cosponsored by the Defense Advanced Research Projects Agency (DARPA) Defense Sciences Office (DSO) and the U.S. Department of Energy (DOE) Office of Civilian and Radioactive Waste Management (OCRWM), is discussed. Programmatic investigations have included a broad range of topics: alloy design and composition, materials synthesis, thermal stability, corrosion resistance, environmental cracking, mechanical properties, damage tolerance, radiation effects, and important potential applications. Amorphous alloys identified as SAM2X5 (Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4) and SAM1651 (Fe48Mo14Cr15Y2C15B6) have been produced as meltspun ribbons (MSRs), dropcast ingots, and thermal-spray coatings. Chromium (Cr), molybdenum (Mo), and tungsten (W) additions provided corrosion resistance, while boron (B) enabled glass formation. Earlier electrochemical studies of MSRs and ingots of these amorphous alloys demonstrated outstanding passive film stability. More recently, thermal-spray coatings of these amorphous alloys have been made and subjected to long-term salt-fog and immersion tests; good corrosion resistance has been observed during salt-fog testing. Corrosion rates were measured in situ with linear polarization, while the open-circuit corrosion potentials (OCPs) were simultaneously monitored; reasonably good performance was observed. The sensitivity of these measurements to electrolyte composition and temperature was determined. The high boron content of this particular amorphous metal makes this amorphous alloy an effective neutron absorber and suitable for criticality-control applications. In general, the corrosion resistance of such iron-based amorphous metals is maintained at operating temperatures up to the glass transition temperature. These materials are much harder than conventional stainless steel and Ni-based materials, and are proving to have excellent wear properties, sufficient to warrant their use in earth excavation, drilling, and tunnel-boring applications. Large areas have been successfully coated with these materials, with thicknesses of approximately 1 cm. The observed corrosion resistance may enable applications of importance in industries such as oil and gas production, refining, nuclear power generation, shipping, etc.

Effect of High Energy Milling Parameters on Nanostructured Cr<sub>3</sub>C<sub>2</sub>-Ni20Cr Powder Characteristics

Cr3C2-NiCr coatings have been used for corrosion and wear resistant applications. In the last decade, thermal sprayed coatings using nanostructured feed stock of other materials has exhibited higher hardness, strength and corrosion resistance. Hence, it is anticipated that nanostructured Cr3C2-NiCr coatings will also exhibit these properties and therefore posses improved performance characteristics. Preparation of nanostructured feed stock powders is the first step in the synthesis of nanostructured coatings and mechanical milling is an effective process to obtain the powders. Preliminary studies in which commercial Cr3C2-NiCr powders were milled in hexane and gaseous nitrogen revealed that particle and crystallite size were significantly smaller in powders milled in nitrogen. This paper presents the effect of hexane content and milling parameters on Cr3C2-Ni20Cr powder characteristics. Use of just sufficient hexane as the milling media reduced significantly the particle and crystallite sizes.

Microstructure and mechanical properties of thermal sprayed nanostructured Cr3C2-Ni20Cr coatings

Cr3C2-Ni20Cr coatings have been used for corrosion and wear resistant applications. However, one of the shortcomings of these coatings is its low hardness, and consequent low wear resistance, for long term high temperature applications. Nanostructured coatings of many materials have exhibited higher hardness and strength compared with conventional coatings of the same material. Consequently, nanostructured coatings of other materials, including Cr3C2-Ni20Cr have been attempted to enhance overall performance. In this study the effects of high energy milling parameters on Cr3C2-25(Ni20Cr) powder characteristics as well as the microstructure and mechanical properties of nanostructured Cr3C2-25(Ni20Cr) coatings formed by high velocity oxygen fuel (HVOF) spraying have been evaluated. The average particle size and crystallite size of milled Cr3C2-25(Ni20Cr) powders decreased with increase in milling time and this decrease was more pronounced in nitrogen compared to that in hexane. This difference has been attributed to a cushioning effect in the latter medium. The coatings prepared with milled Cr3C2-25(Ni20Cr) powders had a more uniform microstructure, were harder and had higher relative fracture toughness compared with coatings prepared with as-received powders.

Duplex Stainless Steels ‐ a Review after DSS ‘07 held in Grado

Duplex stainless have always been an exiting area of interest for researchers, stainless steel producers, fabricators and end users. They present very diversified technical challenges and simultaneously attractive in‐service properties at excellent cost/properties ratios, particularly in critical markets including oil and gas, chemical industry, pulp and paper industry, water systems, desalination plants, pollution control equipments, chemical tankers, etc. This explains why although they still remain a marginal production in the stainless steel business (less than 1%) dedicated international conferences have been organised since about 25 years. The purpose of this paper is to present a review of the 100 scientific contributions presented during the latest international duplex stainless steel conference witch took place in Grado, Italy, on 18‐20 June 2007. The main topics concerned microstructure and mechanical properties, weldability, corrosion resistance and in‐service properties. The “standard” duplex stainless steels, i.e. the 2304, 2205, and the family of 2507 (Cu,W, ...) grades were confirmed as very valuable grades with outstanding performances proven in more than 20 years successful in‐service applications. New grades including the so‐called lean duplex dedicated to volume oriented markets (possible replacement of 304/316 grades) and some “niche” grades dedicated to very specific markets were presented. It was pointed out that the duplex grades start to be well established products particularly suitable for corrosion resistance applications. They show a two‐digit yearly growth thanks to the production of new grades and production ranges (coils and bars) targeting the replacement of the more costly 300 series including 304 but also rusty carbon steel in e.g. structural application.

Microstructural characteristics and mechanical properties of HVOF sprayed NiCrAl coating on superalloys

Abstract High velocity oxy-fuel (HVOF) process sprayed NiCrAl coatings on superalloys were characterized by various techniques such as optical microscopy, X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive spectroscopic analysis (SEM/EDS) to render an insight into their microstrucural features and assess its suitability for high temperature corrosion resistance applications. The as sprayed coatings were found to be dense with splat like layered morphology. The XRD analysis of the coating showed the presence of Ni (fcc) as a prominent phase with Cr and Al as minor phases. The porosity of the coatings was calculated from its optical micrographs and found to be less than 1.7%. The measured hardness and average bond strength of the coatings were found to be in the range of 278–351 Hv and 59 MPa, respectively. The observed microstructral characteristics, higher bond strength, and hardness of HVOF sprayed NiCrAl coating show that it may act as an effective barrier to provide high temperature protection to the superalloys.

Interfacial Microstructure of Chromium Oxide Coatings

Chromium oxide coatings are chemically inert, have high mechanical strength, hardness and good optical characteristics; therefore, they have been widely used in many applications including corrosion protection, wear resistance, electronics, and optics. Cr2O3 is well suited for wear resistance applications, as it is one of the hardest oxides with 29.5 GPa hardness. Several deposition techniques have been tried for making these coatings. Cr2O3 coating hardness can vary substantially due to compositional and microstructural variations, depending on the deposition method. Hardness of a plasma-sprayed Cr2O3 coating, 50 lm thick was about 14.7 GPa, while a 200 nm thick RF-sputtered chromium oxide coating, stoichiometrically close to Cr2O3, exhibited 30 GPa hardness combined with good scratch resistance. Even for the bulk Cr2O3, hardness values reported were from 9 GPa to 29.5 GPa. Hones et al. investigated a correlation between the hardness and the sputtering deposition parameters, i.e. oxygen partial pressure and substrate temperature, and found favorable deposition conditions with an oxygen partial pressure of about 15–20 % of the total sputtering gas pressure at substrate temperatures exceeding 500 K. Good coating adhesion is required for wear and corrosion resistance applications. Premature failure can occur for many reasons including coating delamination, cracking and plastic deformation. In addition to this, thin ceramic PVD coatings usually have columnar grain structure with micro cracks, pinholes, transient grain boundaries and often high throughcoating porosity, which all lead to accelerated pitting corrosion and failure at the coating/substrate interface, especially in hostile environments. On the other hand, several studies showed that coating thickness plays an important role in enhancing both PVD-coated tool cutting performance and resistance to abrasive and erosive wear. Graded systems have been employed to obtain thicker coatings without losing performance in terms of coating adhesion and toughness. It is likely that thicker coatings will improve corrosion resistance in aqueous environments by eliminating through-thickness pin-hole defects. Coating mechanical, adhesion and wear properties are strongly affected by microstructure. Interfaces with high adhesion are known to ensure prolonged coating life and good wear resistance. Sputtered coating microstructure and physical characteristics depend on the deposition parameters. Also, substrate surface conditions prior to deposition, characterized by surface roughness, stress and oxidation state, play an important role in controlling coating properties. In this paper SEM and TEM techniques were used to characterize thicker chromium oxide coating interfacial microstructure as a step towards developing a unique method for depositing thicker coatings with small grains, smooth surface and low residual stress.

The new 200-series: an alternative answer to Ni surcharge? Risks or opportunities?

The paper reviews the 200 series and points out the specificities of the new developed grades. Chemical compositions, mechanical properties, corrosion resistance properties and applications are presented. The lack of international codes for those grades is pointed out. Finally warnings are addressed for improper uses of those grades by end-users.

Mechanical Properties and Corrosion Resistance of a Novel Ni‐Cr‐Mo Alloy

A new Ni-23Cr-18Mo (wt.%) alloy, designated as Nistelle Super C, was developed recently at Deloro Stellite Inc. for high corrosion resistance applications. Microstructure and phase transformation behaviour of the alloy were studied using SEM and DSC techniques, respectively. Mechanical properties such as stress - strain relation of the alloy and load – depth relation of individual phases of the alloy were determined under uniaxial tension and under nano indentation, respectively. Corrosion resistance of the alloy in oxidizing and reducing acids was evaluated in accordance with ASTM standard test designation G31-72.

Stainless steel binder for the development of novel TiC-reinforced steel cermets

Steel reinforced TiC composites are an attractive choice for wear resistance and corrosion resistance applications. TiC-reinforced 17-4PH maraging stainless matrix composites were processed by conventional powder metallurgy (P/M). TiC-reinforced maraging stainless steel composites with >97% of theoretical density were fabricated. The microstructure, mechanical and wear properties of the composites were evaluated. The microstructure of these composites consisted of spherical and semi-spherical TiC particles. A few microcracks appeared in the composites, showing the presence of tensile stress in the composites produced during sintering. Typical properties, namely, hardness and bend strength were reported for the sintered composites. After heat treatment and aging, the increase of hardness was observed. The increase of hardness was attributed to the aging reaction in the 17-4PH stainless steel. The precipitates appeared in the microstructure and were responsible for the increase in hardness. The specific wear behavior of the composites was strongly dependent on the content of TiC particles, the interparticle spacing, and the presence of hard precipitates in the binder phase.

Oxidation-induced strengthening in ground silicon carbide

Silicon carbide has specific advantages over other structural ceramics, such as high temperature capability and excellent chemical stability. So silicon carbide is a promising candidate for high temperature structural materials as well as for corrosion resistance applications. Like brittle materials, however, strength of silicon carbide is closely related to the size and distribution of surface flaws such as machining-induced cracks, because of their inherent low toughness. Thus, a smooth polishing procedure after grinding is often needed in order to reduce the size of surface flaws, leading to an increase in cost of ceramic components. Moreover, the allowable flaws in ceramics are so small that it is almost impossible to detect the flaws and also difficult to remove them completely using machining techniques. As a result, the structural integrity of a ceramic component is seriously affected. A method, to heal a crack, could be considered to overcome this problem. Studies on crack healing have been reported for alumina [1–3], silicon nitride [4–6], silicon nitride/silicon carbide composite [7], Mullite/silicon carbide composite [8] and silicon carbide [9–12]. Our research group recently proposed a mechanism of crack healing and strengthening by pre-oxidation procedure in silicon carbide [11, 12]. The major observation is that the residual stress produced by the thermal expansion mismatch between silica (within cracks) and surrounding silicon carbide played a significant role in the strength increase. As the crack healing technique can be adopted in practical strength applications, considerable advantages can be expected either in the reliability or in the machining and inspection costs of ceramic components. In the above perspectives, the effect of pre-oxidation on strength of silicon carbide with grinding-induced surface cracks was investigated and reported in the present communication. SiC material (Hexoloy, Carborandom, Inc., USA) was received in a plate form. The microstructure of the material consisted of SiC grains smaller than 10 lm and average grain size is about 5 lm (see Fig. 1). The material was machined into flexure specimens of 3 mm · 4 mm · 40 mm. The specimen surface was ground using diamond wheels with girt sizes of 127 lm, 64 lm, 42 lm and 32 lm. Grinding conditions were: 3,300 rpm, 35 m/s peripheral wheel speed and 10 lm depth of cut. The specimens were mounted on a holder in such a manner that grinding was oriented along the width of the specimens (perpendicular to the tensile stresses applied during the strength measurement). The ground specimens were then heat-treated at 1,500 C for 50 h in air. The heating rate was 10 C/min and cooling was done by turning off the electric power of the furnace. For comparison, some heat treatment experiments were also conducted in vacuum under similar conditions. The microstructure was characterized by field-emission scanning electron microscopy (FESEM), Energy Dispersive X-ray (EDX) and X-ray Diffraction (XRD). The strength of specimens was measured using a four-point bending fixture with outer and inner spans of 30 mm and 10 mm, respectively at a crosshead speed of 0.5 mm/min, as per the standard procedure [13]. Specimens were placed in the fixture such that the surface containing grinding-induced cracks was in M. C. Chu (&) AE S. J. Cho AE G. J. Yoon AE H. M. Park Division of Chemical Metrology and Materials Evaluation, Korea Research Institute of Standard and Science, 1 Doryong-dong, Yuseong, Deajeon 305-600, Korea e-mail: chumin@kriss.re.kr

An overall aspect of electroless Ni-P depositions—A review article

Literature on electroless Ni-P deposition, in recent decades, has dwelled primarily on surface engineering and corrosion-resistant applications. By contrast, we have many research articles devoted to the engineering aspects of the electroless Ni-P depositions and their technology. The present article deals with the development of electroless Ni-P bath, advantages and mechanisms of deposition, and applications of the Ni-P deposits. We also present a comparison of the properties of electroless Ni-P and Ni-B as well as the recent developments in nickel-phosphorous research. We attempt to review these in a detailed manner. We also briefly discuss the future developments of electroless Ni-P.

EFFECT OF MICROSTRUCTURE AND PHOSPHORUS CONTENT ON THE CORROSION BEHAVIOUR OF ELECTROLESS NICKEL-PHOSPHORUS COATINGS

The effects of microstructure and phosphorus (P) content on the corrosion characteristics of electroless Ni-P coatings on mild steel in a 3.5 wt% NaCl solution were investigated using a potentiodynamic technique. The results indicate that the anodic and cathodic behaviour of the coatings varied with changes in the structure, morphology and phosphorus contents of the coatings. Different alloy compositions and heat treatment conditions influenced both the microstructural characteristics and crystallization behaviour of the deposit. The addition of thiourea to the electroless plating solution increased the intrinsic stress due to the stabilizing effect on the bath. It is postulated that the coating should enjoy enhanced corrosion resistance for applications where mild steel is in contact with a saline environment.On a étudié les effets de la microstructure et de la teneur en phosphore (P) sur les caractéristiques de corrosion de revêtements de déposition autocatalytique de Ni-P sur l’acier à faible teneur en carbone dans une solution de 3.5% en poids de NaCl, en utilisant une technique potentiocinétique. Les résultats indiquent que les comportements anodique et cathodique des revêtements variaient avec les changements de structure, de morphologie et de teneur en phosphore des revêtements. Différentes compositions d’alliage et différentes conditions de traitement thermique influençaient à la fois les caractéristiques de microstructure et le comportement de cristallisation du dépôt. L’addition de thiourée à la solution de déposition autocatalytique augmentait la contrainte intrinsèque, dû à l’effet de stabilisation du bain. On postule que le revêtement devrait jouir d’une résistance améliorée à la corrosion dans les applications où l’acier à faible teneur en carbone est en contact avec un environnement salin.

Stepping outside the standards for higher corrosion resistance

Traditionally, high-alloy steels have been widely used in corrosion-resistant applications, but with limited success in more severe duties. Around 30 years ago, when austenitic-ferritic steels (duplex) became available, Sulzer Pumps used the material in seawater injection pumps. Arto Riihimaki and Redvers Paley of Sulzer Pumps discuss the advantages that the latest in high-alloy cast steels have over duplex types.

Formation of hard tungsten boride layer by spark plasma sintering boriding

Metal borides are attractive candidates for high-temperature, wear resistance, and corrosion resistance applications. Tungsten borides (WB and W2B5) are known to have high hardness values, chemical inertness, and electronic conductivity, and have potential industrial applications as abrasive, corrosion-resistant and electrode materials, which are exposed to exacting environments. In this work, boride layers are formed on the surface of W samples using a pack boriding method with the assistant of the spark plasma sintering technique. The process was performed in the temperature range 1000–1400 °C with a holding time of 30 min. The microstructure, microhardness, and fracture toughness of the tungsten boride layer are investigated by optical microscopy, X-ray diffraction and microhardness indentations. Results showed that the boride layer, composed of WB, have thickness in the range ∼35–112 μm. The WB layers are found to have a preferred orientation in the (200) direction, which is reflected by a distinct columnar growth observed in the optical micrographs of polished cross-sections of SPS samples.

Vinyl esters lead the corrosion challenge

50 years of in-service experience means composites are no longer considered ‘the last resort’ for corrosion resistant applications. Amanda Jacob reports on how the latest developments in vinyl ester resins are helping to advance composites into even more applications. Amanda Jacob reports.

Development of an Aluminized Multi‐Phase Steel with Dual Phase Properties for High Temperature Corrosion Resistance Applications

A high strength, high Mn, Cr‐Mo containing multi‐phase steel grade was aluminized with a 90 wt% Al – 10 wt% Si alloy coating, using a laboratory hot‐dip simulator. The adhesion of the coating to the steel strip was evaluated and the microstructure of the as deposited material was assessed. The coated sheet steel was tested at high temperatures by monitoring the weight gain of the samples and their mechanical properties as a function of time. It was found that the thermal properties of the aluminized sheet were excellent. The analysis of the coating/substrate interface revealed the dissolution of brittle intermetallic phases, explaining the excellent high temperature resistance performance of the Al‐Si coating up to temperatures as high as 900°C. In addition, the use of a continuous annealing cycle common in current aluminizing lines, resulted in a dual phase microstructure.

Mastering the tests of time

Mark Seibert, global business director for composites at Dow, presents a brief history of DERAKANE, a resin which has been providing solutions in corrosion-resistant applications for the last 40 years.

Early stages of interface reactions between AlN and Ti thin films

The early stages of interface reactions between AlN and Ti thin films were investigated using x-ray diffractions, Auger electron spectroscopy, cross section transmission electron microscopy (XTEM), and high resolution XTEM. The AlN/Ti bilayers were deposited on a molybdenum substrate using reactive and nonreactive magnetron sputtering techniques. After deposition, the bilayers were heat treated for 1–10 h at 600 °C in a nitrogen atmosphere. Decomposition of the AlN layer took place at the AlN/Ti interface and its products, Al and N, reacted with Ti to produce a AlN/Al3Ti/Ti2N/Ti3Al/α-(Ti, Al)ss phase sequence. This phase sequence is not consistent with the Ti–Al–N phase diagram and is believed to be the outcome of the particular conditions that prevail in the thin film and correspond to a particular set of kinetic parameters. A model that explains the development of the phase sequence and predicts its evolution after prolonged heat treatments is put forward. The applicability of such a solid-state reaction technique for producing functionally graded coating for wear and corrosion resistance applications is discussed.

Structural characterization of laser-treated Cr3C2–NiCr coatings

The interconnected porosity of the Cr3C2–NiCr coatings obtained by high-velocity oxy fuel spraying is detrimental in corrosion and wear resistance applications. Laser treatments allow sealing of their surfaces through melting and resolidification of a thin superficial layer. A Nd:YAG laser beam was used to irradiate Cr3C2–NiCr coatings either in the continuous wave mode or at different repetition rates in the pulsed one. Results indicated that high peak and low mean laser irradiances are not good, since samples presented deep grooves and an extensive crack network. At low peak and higher mean laser irradiances the surface was molten, and only a few shallow cracks were observed. The interconnected porosity was completely eliminated in a layer up to 80 μm thick, formed by large Cr7C3 grains imbedded in a NiCr matrix.

ALLEGHENY LUDLUM TYPE 201L

Abstract Type 201L is a low carbon version of type 201, an austenitic Cr-Ni-Mn stainless steel. It maintains satisfactory intergranular corrosion resistance in applications involving welding, particularly heavier gage material. This datasheet provides information on composition, physical properties, hardness, and tensile properties. It also includes information on corrosion resistance as well as heat treating. Filing Code: SS-825. Producer or source: Allegheny Ludlum Corporation.