NiAl Bronze Research Articles

An Environmentally Assisted Cracking Evaluation of UNS C64200 (Al–Si–Bronze) and UNS C63200 (Ni–Al–Bronze)

A recent failure of a union nut, UNS C64200, made of Al–Si–Bronze (ASB) in a breathing air system of a marine platform has highlighted the need for environmentally assisted cracking (EAC) data for both ASB and Ni–Al–Bronze UNS C63200 (NAB) components in environments relevant to marine use. In addition, the possibility of exposure to ammonia environments via cleaning agents or biological processes warrants consideration because of the known susceptibility of bronze to EAC in ammonia environments. A displacement-controlled, rising step load (RSL) technique was employed on precracked compact tension specimens to quantify and compare the threshold stress intensities for EAC in air, seawater (SW), and SW + ammonia environments for wrought ASB and NAB materials. These results are compared to calculations of the stress intensity in service to determine the probability of EAC initiation. ASB was found to be susceptible to subcritical intergranular EAC initiation in laboratory air, SW, and SW + ammonia environments. NAB was immune to EAC under the conditions tested in laboratory air and SW, but was susceptible to intergranular EAC in SW + ammonia solution. The threshold stress intensity in SW + ammonia was found to be similar for both ASB and NAB; however, the subcritical crack growth rate for NAB was found to be 2–3 times faster than ASB. Calculations of stress intensity indicate that, in the air system applications where the installation torques are higher, the likelihood of subcritical cracking in ammonia environments is high. Stress intensities approach the ASB threshold values for subcritical intergranular cracking in air when the defect depth approaches half the wall thickness of the nut.

Evaluation of Stress Environment around Pits in Nickel Aluminum Bronze Metal under Corrosion and Cyclic Stresses

Surface damage in the form of pitting was observed in NiAl Bronze metal subjected to corrosion and cyclic stresses. In order to investigate the stresses surrounding the evolving pits due to corrosion, an image based computational study was carried out. The computational study involves developing an analysis model from the SEM images of corroded pits and then conducting stress analysis. Several computational simulations were carried out with increasing/evolving pits and the corresponding stress environment was obtained. The results obtained indicate that pit profiles (size and height) greatly affect the stress environment and the maximum stresses may vary depending on the pit profile. Overall, the results obtained illustrate that the stress environments around pit profiles are non-uniform and can attain maximum values at various locations around the pits due to non-uniformity of pit profiles in NAB metal. From these stresses, it is possible to predict where the cracks (Mode I and Mode II) or mixed mode (Mode I & II) may initiate from the pit profiles in the material.

Strengthening Mechanisms in NiAl Bronze: Hot Deformation by Rolling and Friction-Stir Processing

Abstract Microstructures produced by isothermal hot rolling of a NiAl bronze material were evaluated by quantitative microscopy methods and parameters describing the contributions of precipitate dispersions, grain size, solute content, and dislocation density to the yield strengths of the individual constituents of microstructure were determined. Models for the strengths of the individual constituents were combined to predict the temperature dependence of the yield strength as a function of hot rolling temperature, and the prediction was found to be in good agreement with measured yield strengths. The models were applied to microstructures in a stir zone produced by multipass friction-stir processing (FSP) and, again, found to predict measured yield strengths with high accuracy. Such models may aid in assessing the role of microstructure gradients produced during FSP and other processes.

Friction Stir Processing (FSP) of Cast Metals: Processing - Microstructure - Property Relationships

FSP is an allied technology of friction stir welding (FSW). These processes are reviewed and the additional considerations such as processing pattern and step over distance in FSP are introduced. The application of FSP to cast metals including AA5083, Al-7Si and NiAl bronze is summarized. As-cast microstructures may be converted to a wrought condition in the absence of external shape change and the extent of grain refinement and homogenization of microstructure is documented. The FSP-induced superplastic response of AA5083, enhanced ductility of Al-7Si and surface hardening of NiAl bronze are summarized as examples of properties developed by FSP.

Optimization of Welding Parameters for Repairing NiAl Bronze Components

The objective of this study is to determine an optimal welding procedure that can be implemented to repair damaged Nickel Aluminium Bronze (NAB) components. NAB is commonly used in marine applications where components are subject to a constant corrosive environment and high stresses. Research into ideal NAB microstructure for a marine application, was performed in order to gain a baseline for experimental analysis of potential welding procedures. The results indicated that the welding repair can be performed with a wide range of heat input. The effect of post-weld heat treatment (PWHT) on the microstructure and mechanical properties in the heat affected zone (HAZ) and weld metal was also investigated in this research. The dominant microstructure in weld metal at as-welded condition is coarse Widmanstatten type structure with high hardness; post-weld heat treatment resulted in significant grain refinement and hardness reduction in weld metal.

Corrosion and Corrosion Fatigue Characteristics of Cast NAB Coated with NAB by HVOF Thermal Spray

Cast Ni-Al bronze (NAB) alloy, which is a most common material of ship propeller operating in sea water, is coated with the same NAB alloy by high-velocity oxy-fuel (HVOF) thermal spray process. Application of a HVOF NAB coating to cast NAB can be considered to enhance the resistance to corrosion fatigue failure of a NAB-based ship propeller and repair its damaged location at low cost. Linear sweep voltammetries, potentiostatic corrosion tests, and 80-day immersion corrosion tests are conducted in a 3.5% NaCl solution to investigate the corroding behavior of HVOF-NAB-coated cast NAB. Corrosion pits and microcracks through which the NaCl solution can easily permeate are developed from many pores included in the HVOF NAB coating. More serious corrosion compared to uncoated cast NAB occurs with producing corrosion products of Cu2O, Al2O3, and Fe2O3. Corrosion fatigue tests of both HVOF-NAB-coated cast NAB and uncoated cast NAB for reference are also conducted in the NaCl solution. Corrosion fatigue strength of the HVOF-NAB-coated cast NAB is measured as 140 MPa, which is much higher than 90 MPa of the uncoated cast NAB.

The Effect of Concurrent Straining on Phase Transformations in NiAl Bronze During the Friction Stir Processing Thermomechanical Cycle

Equivalent strains up to a value of ≈2.7 were determined by evaluation of the shape changes of the phases in a duplex α(fcc)/β(bcc) microstructure formed ahead of the pin tool extraction site during the friction stir processing (FSP) thermomechanical cycle in a cast NiAl bronze alloy. Correlation of the local strains with volume fractions of the various microstructure constituents in this alloy shows that the concurrent straining of FSP results in acceleration of the α + β → β reaction in the thermomechanically affected zone (TMAZ) ahead of the pin extraction site. The resulting volume fraction of β (as determined by the volume fraction of its transformation products formed during post-FSP cooling) corresponds closely to the volume fraction expected for the peak stir zone temperature measured separately by means of thermocouples embedded within the tool pin profile along the tool path. The stir zone (SZ) in this material exhibits near-equilibrium microstructures despite brief dwells near the peak temperature (T peak ≈ 0.95T melt), reflecting large local strains and strain rates associated with this process.

Effect of Multiple-Pass Friction Stir Processing Overlapping on Microstructure and Mechanical Properties of As-Cast NiAl Bronze

As-cast Cu-9Al-4.5Ni-4Fe NiAl bronze alloy (NAB) was subjected to multiple-pass friction stir processing (FSP) with a 50 pct overlap. After FSP, the coarse microstructure of the base metal (BM) was transformed to defect-free material with fine microstructure. While the torchlike patterns in the stir zone (SZ) and the uplifted grains in the transitional zones (TZs) between two passes were observed in the multiple-pass FSP region, no grain coarsening was found in the remnant zone of the previous SZ after subsequent FSP pass. The hardness value of the FSP materials was higher than that of the BM and was homogeneously distributed throughout the entire multiple-pass FSP region. The FSP materials showed greatly improved tensile properties compared to the BM, and the TZs showed similar tensile strength and ductility to the single-pass FSP materials. The BM broke in a mixture mode of brittle cleavage and microvoid coalescence fracture, whereas the FSP and TZ samples failed in the latter fracture mode. The results showed that the multiple-pass overlapping (MPO) FSP was feasible to modify the microstructure of large-sized plate of the NAB.

Influence of Phosphorus Concentration and Heat Treatment on Anticavitation Erosion Characteristics in Electroless Nickel Plating

Cavitation erosion has been a serious problem in the use of turbomachineries such as ship propellers. In this paper, we proposed a technique to prevent cavitation erosion using electroless nickel-phosphorus plating (ENP). ENP was plated on JIS CAC703 (Ni-Al Bronze), which is known as a material of ship propellers. We examined the anticavitation property of ENP by a vibratory cavitation apparatus based on ASTM G32. It was found that the mass loss of plated substrate can be decreased ten times less than that of substrate by selecting suitable heat treatment temperature for the concentration of phosphorus in ENP. Finally, the mechanism of erosion of ENP is discussed.

Classification of corrosion defects in NiAl bronze through image analysis

Corrosion surface damage in the form of pitting and micro-cracks is observed in many metals. Cracks usually initiate from the pits and grow under cyclic stresses and eventually lead to material failure. An image analysis based on wavelet transforms and fractals was used to study the corrosion morphology of nickel aluminum bronze metal under varying corrosion conditions and applied stresses. Image feature parameters were extracted and analyzed to classify the pits/cracks in the metal samples. The results obtained indicate that classification of pits/cracks is possible with image analysis and may be used for correlating service/failure conditions based on corrosion morphology.

Corrosion properties of friction–stir processed cast NiAl bronze

Friction–stir processing (FSP) was adopted to modify the microstructure of a cast Cu–9Al–4.5Ni–4Fe NiAl bronze alloy (NAB). After FSP, the initial coarse microstructure of the cast NAB was transformed to a fine structure, and the porosity defects were eliminated. The microstructure modification changed the corrosion behavior of the NAB in a 3.5% NaCl solution. In a static immersion corrosion test, the FSP NAB exhibited significantly greater corrosion resistance compared to the cast counterpart. The polarization curve and electrochemical impedance spectroscopic (EIS) results indicated that the FSP NAB showed slightly lower electrochemical corrosion resistance.

Friction Stir Processing (FSP) of Cast Metals: Microstructure – Property Relationships in NiAl Bronze and AA5083

Parameters for multi-pass FSP include the pattern of tool traverse and step-over distance between successive passes. Multi-pass FSP was conducted on as-cast NiAl bronze and as-cast AA5083 in order to modify stir zone (SZ) microstructures and mechanical properties. Highly refined and homogeneous SZ microstructures may be produced by FSP. Refined and equiaxed grain structures reflect recrystallization during FSP; mechanisms leading to homogenization by redistribution of microstructure constituents remain to be determined. Refined microstructures exhibit enhanced ambient-temperature properties and superplasticity at elevated temperatures.

Peak Stir Zone Temperatures during Friction Stir Processing

The stir zone (SZ) temperature cycle was measured during the friction stir processing (FSP) of NiAl bronze plates. The FSP was conducted using a tool design with a smooth concave shoulder and a 12.7-mm step-spiral pin. Temperature sensing was accomplished using sheathed thermocouples embedded in the tool path within the plates, while simultaneous optical pyrometry measurements of surface temperatures were also obtained. Peak SZ temperatures were 990 °C to 1015 °C (0.90 to 0.97 T Melt) and were not affected by preheating to 400 °C, although the dwell time above 900 °C was increased by the preheating. Thermocouple data suggested little variation in peak temperature across the SZ, although thermocouples initially located on the advancing sides and at the centerlines of the tool traverses were displaced to the retreating sides, precluding direct assessment of the temperature variation across the SZ. Microstructure-based estimates of local peak SZ temperatures have been made on these and on other similarly processed materials. Altogether, the peak-temperature determinations from these different measurement techniques are in close agreement.

Inhomogeneous microstructure and mechanical properties of friction stir processed NiAl bronze

As-cast Cu–9Al–4.5Ni–4Fe NiAl bronze (NAB) alloy was subjected to friction stir processing (FSP) in a wide range of tool rotation rates of 800–2000 rpm and traverse speeds of 50–200 mm/min. After FSP, the initial coarse microstructure of the as-cast NAB was transformed to fine structure, and the porosity defects were eliminated. However, the stir zones were characterized by inhomogeneous structure and could be divided into four regions: fine Widmanstätten primary α phase in the surface layer, banded primary α and β′ phases in the subsurface layer, equiaxed α and β′ phases in the center, and streamlike α and β′ phases at the bottom. The heterogeneous microstructure could be alleviated by adjusting the FSP parameters, but could not be completely eliminated under investigated FSP parameters. The FSP NAB exhibited significantly improved hardness, tensile strength, and ductility compared to the base metal. When the NAB was subjected to two pass FSP, its microstructure was further homogenized, resulting in apparently increased ductility with similar hardness and tensile strength.

The effect of low-dose neutron irradiation on mechanical properties, electrical resistivity and fracture of NiAl bronze for ITER

Nickel–aluminum bronze is a candidate material for several applications for ITER in-vessel components such as divertor and blanket attachments and remote handling equipment. This paper presents the first results of an experimental investigation of the effect of neutron irradiation on mechanical properties, fracture characteristics and electrical resistivity of NiAl bronze. Specimens of NiAl bronze were irradiated at 150 °C and 300 °C to doses of 10 −3; 10 −2; 0.7 ∗ 10 −1 dpa in the RBT-6 reactor ( Φt therm/ Φt fast ∼ 1) in Dimitrovgrad. It was shown that irradiation at 150 °C leads to minor changes of tensile properties, whereas irradiation at 300 °C results in significant loss of ductility at damage dose of 0.07 dpa. The change of electrical resistively of NiAl bronze is low, ≈3% at the maximum dose studied. The reasons for the high-radiation resistance of NiAl bronze in comparison with copper and copper alloys are discussed.

Controlled Plasticity Burnishing to Improve the Performance of Friction Stir Processed Ni-Al Bronze

Friction stir welding (FSW) allows the joining of aluminum alloys in ways previously unattainable offering new manufacturing technology. Friction stir processing (FSP) of cast alloys such as Ni-Al bronze eliminates casting voids and improves the properties to that of wrought material. However, the local heating produced by both FSW and FSP can leave a fusion zone with reduced mechanical properties and a heat-affected zone with tensile residual stresses that can be deleterious to fatigue performance. Controlled plasticity burnishing (CPB) is an established surface treatment technology that has been investigated and described extensively for the improvement of damage tolerance, corrosion fatigue, and stress corrosion cracking performance in a variety of alloys. Mechanical CPB processing in conventional CNC machine tools or with robotic tool positioning is readily adapted to industrial FSW and FSP fabrication of components, either simultaneously or as a post process. CPB was applied to FSP Ni-Al Bronze to produce a depth of compression of 2.5 mm and a maximum subsurface magnitude of –150 ksi. The effect of FSP on the fatigue performance in a saltwater marine environment and in the presence of foreign object damage (FOD) was documented with and without CPB processing. FSP was found to increase the fatigue strength of the Ni-Al Bronze by 70% without affecting the corrosion behavior of neutral salt solution. FSW actually produced a more noble material in the acidic salt solution. CPB after FSP mitigated damage 1 mm deep.

Tensile and Fatigue Properties of Friction Stir Processed NiAl Bronze

Friction stir processing (FSP) produced local microstructural refinement in cast Ni Al Bronze. The refined microstructure quality was evaluated with mechanical property characterization using monotonic tension and fatigue testing as a function of FSP raster patterns. Modifying the cast NiAl bronze with FSP resulted in a 140 - 172 % increase in yield strength, and a 40 - 57% increase in tensile strength. Changing the raster pattern from a linear to a rectangular spiral raster increased the tensile elongations by 40 - 134%. This increase in elongation was attributed to increased microstructural uniformity through the depth of the FSP raster. The ability to transfer FSP technology was demonstrated with consistent tensile property data produced by three different laboratories. Fatigue characterization (both uniaxial and rotating-bending fatigue) showed that FSP improved the cast NiAl bronze fatigue resistance. Both types of fatigue testing showed differences in fatigue resistance as a function of processing parameters.

Friction Stir Processing of Cast NiAl Bronze

Friction stir processing (FSP) of cast NiAl bronze has resulted in significant increases in properties including more than doubling the yield greater that 40 percent increase in the threshold fatigue life; all achieved while increasing ductility. These and other strength, greater than a 60 percent increase in tensile strength, and property improvements were realized following studies of FSP procedures specifically for NiAl bronze. Within this manuscript, FSP procedures and other “lessons learned” are presented. Details of property improvements are documented elsewhere within this conference proceedings (see Fuller et al.). Presented herein are tool designs for efficient material flow, tool materials capable of long life at 1000°C, rastering procedures covering large surface areas, and other results pertinent to achieve improved properties in cast NiAl bronze following friction stir processing.

Microstructure Evolution and Microstructure-Property Relationships in Friction Stir Processing of NiAl Bronze

Friction stir processing (FSP) has been employed for localized modification and control of microstructures in NiAl bronze materials, which are widely utilized for marine components. The thermomechanical cycle of FSP results in homogenization and refinement and the conversion of microstructures from a cast to a wrought condition within stir zones in the material. However, the direct measurement of stir zone temperatures, strains, strain rates and cooling rates is difficult due to steep gradients and transients in these quantities, and this is an impediment in the assessment of FSP-induced microstructures and properties. Quantitative microstructure analyses following FSP of cast NiAl bronze materials have been used to develop estimates of stir zone thermomechanical cycles. The estimation procedures will be reviewed and the microstructure-based estimates will be compared to results from computational models and embedded thermocouples measurements. Stir zone microstructures comprise a mixture of primary α grains and transformation products of the β that formed during processing. Recrystallization in the primary α occurred due to particle-stimulated nucleation in this low stacking fault energy material. Factors that influence the distribution of strength and ductility in the stir zone appear to include the mixture of microstructure constituents and gradients in microstructure due to gradients in processing conditions.

Microstructural transformations and mechanical properties of cast NiAl bronze: Effects of fusion welding and friction stir processing

A plate of as-cast NiAl bronze (NAB) material was sectioned from a large casting. A six-pass fusion weld overlay was placed in a machined groove; a portion of the weld reinforcement was removed by milling and a single friction stir processing (FSP) pass was conducted in a direction transverse to the axis of and over the weld overlay. A procedure was developed for machining of miniature tensile samples and the distributions of strength and ductility were evaluated for the fusion weld metal; for the stir zone (SZ) produced by the friction stir processing; and for a region wherein friction stir processing had taken place over the fusion weld. A region of low ductility in the heat affected zone (HAZ) of the fusion weld and in the thermomechanically affected zone (TMAZ) of friction stir processed material was attributed to partial reversion of an equilibrium lamellar eutectoid constituent upon local heating above ∼800 °C and formation of non-equilibrium transformation products upon subsequent cooling. The adverse effect on ductility is worse in the heat affected zone of the fusion weld than in the thermomechanically affected zone of friction stir processing due to the lower heat input of the latter process. The implications of this work to engineering applications of friction stir processing are discussed.