High-boron Alloy Research Articles

Study on Mechanical Properties and Microstructure of High Boron Alloy

The mechanical properties and microstructure of high boron alloy (HBA) with different content of boron and carbon were investigated using Taguchi method for obtaining the optimized composition. In addition, the effect of modification with different RE content and the effect of heat treatment on the alloy were studied as well. Results show that the optimized chemical compositions of the HBA are as follows: 0.5% C、3.0% B、1.0% Si、1.0% Mn、1.0% Cu、1.5% Cr、0.5% V and the rest is Fe, and the best content of the RE are 0.8%-1.0%. After the modification and the heat treatment, the mechanical properties of alloy improve significantly. This is because that the matrix of alloy is changed from pearlite to martensite, and the network of boride is broken up and distributed more evenly to form an isolated and discontinuous distribution. The alloy with this composition has been successfully used for anode claw in aluminum smelter, which greatly improves the wear resistance.

The effect of boron on the wear behavior of iron-based hardfacing alloys for nuclear power plants valves

The effect of boron of Fe–Cr–C–Si alloys, replacing Stellite 6 traditionally used in nuclear power industry, on the high temperature wear resistance was characterized. Sliding wear tests of Fe–Cr–C–Si–xB (x=0.3, 0.6, 1.0 and 2.0wt%) alloys were performed in air at temperatures ranging from 300 to 725K under a contact stress of 103MPa. Low-boron alloys containing less than 0.6wt% boron showed the excellent wear resistance than any other tested alloys in an elevated temperature. The improvement was associated with the matrix hardening by promotion of the γ→α′ strain-induced martensitic transformation occurred during wear. In addition, protective oxide layers formed on the contacting surface reduced the wear loss by minimizing the direct metal-to-metal contact. However, high-boron alloys containing more than 1wt% boron showed somewhat larger amount of wear loss than low-boron alloys due to the absence of the strain-induced martensitic transformation and the presence of the brittle FeB particles connected with easy crack initiation.

The effect of solidification conditions on phase transformation of iron matrix of Fe-25mass%Cr-C-B alloys

M2B, M23(C,B)6 and M7(C,B)3 compound phases which constitute the eutectic structures of Fe-25mass%Cr-C-B alloys vary depending on both carbon and boron content. The composition of the matrix structure also varies with each eutectic structure. Due to this, it is presumed that the transformation behavior of the matrix is affected by the solidification rate of the cast material. In the present research, three kinds of molds are used in changing the solidification rate, namely, an exothermic mold, a sand mold and a metal mold. The alloys made from each mold are subjected to thermal expansion tests in order to clarify the transformation behavior both in furnace cooling and air cooling conditions. The results indicate that the hardness of each alloy is higher in a mold where solidification is faster. Most of the alloy transform to martensite during air cooling. In furnace cooling, low carbon with high boron alloys transform to bainite, whereas, high carbon alloys transform to pearlite. Furthermore, alloys with lower carbon content have ferritic matrix which does not transform to any other structure in any cooling condition.

The microstructure of fast neutron irradiated Nimonic PE16

The microstructures of a number of conditions of Nimonic PE16, irradiated in EBR-II at temperatures from 394 to 636°C to displacement doses up to 74 dpa, have been examined. Volume changes, determined from density measurements, were less than 1% in the solution treated and aged (STA) and overaged (OA) conditions. Specimens which were cold worked by 20% or more prior to aging exhibited no significant void swelling. Redistribution of γ′ to point defect sinks occurred, particularly at higher temperatures, resulting in a skeletal γ′ form in both the STA and OA conditions. In cold worked conditions the γ′ precipitates tended to retain a more equi-axed shape. Continuous grain boundary layers of γ′ were produced in STA PE16 at intermediate irradiation temperatures. Grain boundary precipitation of M 6C and Laves phase occurred at higher temperatures and was more prevalent in a high-boron alloy. Mass spectrometry measurements confirmed that the helium generation rate in PE16 was about 1.2 appm per dpa, and assessments of the total helium contents of gas bubbles yielded a value for the bubble surface energy of 3 J m −2. The mechanism of irradiation embrittlement in PE16 is discussed in the light of these observations.

Microstructural change upon annealing FeZrB alloys with different boron contents

To clarify the reason for the change in effective permeability with increasing boron content before and after crystallization, we investigated the microstructure of Fe 93− x Zr 7B x ( x = 2, 4, 6, 8) alloys annealed for 1 h in the temperature range 350–600 °C, using transmission electron microscope. In low boron alloys ( x = 2, 4), the amorphous phase showed indications of a typical interconnected pattern, exhibiting a spinodal-type decomposition. After crystallization, it changed to a mainly single b.c.c. structure with a homogeneous grain size distribution of about 20 nm, and the effective permeability had a high value of around 19000. In high boron alloys ( x = 6, 8), the microstructure after crystallization showed an inhomogeneous grain size distribution, and a low effective permeability. These results may be the result of the different phase separation pattern in the amorphous state.

The stress-induced instability of grain boundary helium bubbles

The microstructures of a number of conditions of Nimonic PE16, irradiated in EBR-II at temperatures from 394 to 636°C to displacement doses up to 74 dpa, have been examined. Volume changes, determined from density measurements, were less than 1% in the solution treated and aged (STA) and overaged (OA) conditions. Specimens which were cold worked by 20% or more prior to aging exhibited no significant void swelling. Redistribution of γ′ to point defect sinks occurred, particularly at higher temperatures, resulting in a skeletal γ′ form in both the STA and OA conditions. In cold worked conditions the γ′ precipitates tended to retain a more equi-axed shape. Continuous grain boundary layers of γ′ were produced in STA PE16 at intermediate irradiation temperatures. Grain boundary precipitation of M6C and Laves phase occurred at higher temperatures and was more prevalent in a high-boron alloy. Mass spectrometry measurements confirmed that the helium generation rate in PE16 was about 1.2 appm per dpa, and assessments of the total helium contents of gas bubbles yielded a value for the bubble surface energy of 3 J m−2. The mechanism of irradiation embrittlement in PE16 is discussed in the light of these observations.

Wear resistance of metastable Ni-B alloys produced by chemical vapor deposition

A manufacturing application of the chemical vapor deposition of nickel from Ni(CO) 4 is the near-net-shape production of high-quality mold or die forms. In certain high wear applications, e.g. transfer molding of a glass-filled epoxy, erosive wear of the nickel die can compromise dimensional control of the product. We have investigated the atmospheric pressure deposition (at 150–155°C) of Ni-B from Ni( CO) 4 + B 2 H 6 gas mixtures in order to develop alloys with improved hardness and wear resistance. The as-deposited alloys are metastable solid solutions of boron in nickel and contain up to 37 at.% B. Evaluations of the alloys in the as-deposited and annealed states have included micro-indentation hardness and 1000-cycle pin- on-disc wear and friction studies using glass-filled epoxy pins. Two high boron alloys are shown to provide excellent resistance to wear when sliding against the glass-filled epoxy.

Soviet superalloy ZHS6-K, effect of B/C modification

A Soviet nickel base cast superalloy, ZHS6-K, has been examined for its response to B/C modification. Three alloy chemistry variants, with 0.17C/0.02B, 0.06C/0.1 B and 0.03C/0.2B (wt%) have been investment cast and investigated for microstructure, heat-treatment, tensile properties, stress-rupture properties and hot corrosion resistance. The B/C modification of the alloy results in some improvement in the yield strength. However, the tensile ductility and the stress-rupture properties are considerably degraded. The nature of the hot corrosion is of a pitting type for the ZHS6-K, whereas it is of a broad front type for the high boron alloys.

Structure and properties of C?B?Fe hard facing alloys

1. Electrospark facing with P/M wire containing boron carbide in the core makes it possible to obtain facings with a high boron content. 2. A high concentration of boron and carbon in iron-base alloys permits the formation of a substantial amount of finely dispersed precipitates of resistant and refractory borides and carbides. 3. The high-boron alloy (4) of the C−B−Fe system has a good combination of properties suitable for the operating conditions of petroleum equipment.

Effect of Melting and Casting Atmospheres on Cast Nickel Alloys

In the past, improvement of heat-resistant cast alloys was dependent upon new compositions. By contrast, this work is directed toward determining the effect of melting and casting atmospheres on the properties of existing nickel base alloys, particularly their rupture strength and elongation at elevated temperatures. Increased strength was most pronounced in high-boron alloys of the Guy type, while improvement in ductility was apparent in all cases.