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1.
The results of a recent study of the effects of ternary alloying with Ti on the fatigue and fracture behavior of a new class
of forged damage-tolerant niobium aluminide (Nb3Al-xTi) intermetallics are presented in this article. The alloys studied have the following nominal compositions: Nb-15Al-10Ti
(10Ti alloy), Nb-15Al-25Ti (25Ti alloy), and Nb-15Al-40Ti (40Ti alloy). All compositions are quoted in atomic percentages
unless stated otherwise. The 10Ti and 25Ti alloys exhibit fracture toughness levels between 10 and 20 MPa√m at room temperature.
Fracture in these alloys occurs by brittle cleavage fracture modes. In contrast, a ductile dimpled fracture mode is observed
at room-temperature for the alloy containing 40 at. pct Ti. The 40Ti alloy also exhibits exceptional combinations of room-temperature
strength (695 to 904 MPa), ductility (4 to 30 pct), fracture toughness (40 to 100 MPa√m), and fatigue crack growth resistance
(comparable to Ti-6Al-4V, monolithic Nb, and inconnel 718). The implications of the results are discussed for potential structural
applications of the 40Ti alloy in the intermediate-temperature (∼700 °C to 750 °C) regime. 相似文献
2.
H. Choe J. H. Schneibel R. O. Ritchie 《Metallurgical and Materials Transactions A》2003,34(2):225-239
The need for structural materials with high-temperature strength and oxidation resistance coupled with adequate lower-temperature
toughness for potential use at temperatures above ∼1000 °C has remained a persistent challenge in materials science. In this
work, one promising class of intermetallic alloys is examined, namely, boron-containing molybdenum silicides, with compositions
in the range Mo (bal), 12 to 17 at. pct Si, 8.5 at. pct B, processed using both ingot (I/M) and powder (P/M) metallurgy methods.
Specifically, the oxidation (“pesting”), fracture toughness, and fatigue-crack propagation resistance of four such alloys,
which consisted of ∼21 to 38 vol. pct α-Mo phase in an intermetallic matrix of Mo3Si and Mo5SiB2 (T2), were characterized at temperatures between 25 °C and 1300 °C. The boron additions were found to confer improved “pest”
resistance (at 400 °C to 900 °C) as compared to unmodified molybdenum silicides, such as Mo5Si3. Moreover, although the fracture and fatigue properties of the finer-scale P/M alloys were only marginally better than those
of MoSi2, for the I/M processed microstructures with coarse distributions of the α-Mo phase, fracture toughness properties were far superior, rising from values above 7 MPa √m at ambient temperatures to almost
12 MPa √m at 1300 °C. Similarly, the fatigue-crack propagation resistance was significantly better than that of MoSi2, with fatigue threshold values roughly 70 pct of the toughness, i.e., rising from over 5 MPa √m at 25 °C to ∼8 MPa √m at 1300 °C. These results, in particular, that the toughness and cyclic
crack-growth resistance actually increased with increasing temperature, are discussed in terms of the salient mechanisms of
toughening in Mo-Si-B alloys and the specific role of microstructure. 相似文献
3.
Gang Duan Donghua Xu William L. Johnson 《Metallurgical and Materials Transactions A》2005,36(2):455-458
We report in this article that strip-shaped amorphous samples with thicknesses from 0.5 to 2 mm were successfully synthesized
for binary Cu-Hf alloys containing 60 to 68 at. pct Cu by the traditional copper mold casting method. The best glass former
Cu66Hf34 with casting thickness up to 2 mm has an undercooled liquid region (ΔT=T
x
−T
g
, where T
g
is the glass transition temperature and T
x
is the onset temperature of the first crystallization event) of 51 K, which is somewhat narrow compared with other neighboring
alloys in the same system. The bulk glassy Cu66Hf34 alloy exhibits Vicker’s Hardness (H
v
) ∼779 kg/mm2, Young’s modulus ∼108 GPa, fracture strength ∼2.1 GPa, and an almost constant elastic elongation ∼1.8 pct upon compression.
The discovery of Cu66Hf34 as a bulk glass confirms the existence of rather simple bulk-glass-forming metallic systems. Moreover, the present Cu-Hf
alloys may be the highest copper content bulk metallic glasses reported to date, to the best of our knowledge. 相似文献
4.
D. L. Davidson K. S. Chan R. Loloee M. A. Crimp 《Metallurgical and Materials Transactions A》2000,31(4):1075-1084
The fatigue and fracture resistance of a commercially made, single-phase Nb-base alloy with 35 at. pct Ti, 5 at. pct Cr, 6
at. pct Al, and several elements to increase solid solution strengthening have been investigated. The threshold for fatigue
crack growth was determined to be ≈7 MPa√m and fracture toughness ≈35 MPa√m. Crack growth was intermittent and sporadic; the
fracture path was tortuous, crystallographic, and appeared to favor the {100} and {112} planes. Fatigue crack closure was
measured directly at the crack tip. The fatigue and fracture properties of the commercial alloy are compared against those
of Nb-Cr-Ti and Nb-Cr-Ti-Al alloys. The comparison indicated that Ti addition is beneficial for, but Al addition is detrimental
to, both fracture toughness and fatigue crack resistance. 相似文献
5.
The present study compares the fatigue and fracture properties of the high-strength β titanium alloy β-Cez with the conventional α+β titanium alloy Ti-6Al-4V, because of increasing interest in replacing α+β titanium alloys with β titanium alloys for highly stressed airframe and jet engine components. This comparison study includes the Ti-6Al-4V alloy
in an α+ β-processed condition (for a typical turbine blade application) and the β-Cez alloy in two distinctly different α+β-processed and β-processed conditions (optimized for a combination of superior strength, ductility, and fracture toughness). The comparison
principally showed a much lower yield stress for Ti-6Al-4V (915 MPa) than for both β-Cez conditions (1200 MPa). The Ti-6Al-4V material also showed the significantly lower high-cycle fatigue strength (resistance
against crack initiation) of 375 MPa (R=−1) as compared to the β-Cez alloy (∼600 MPa, R=−1). Particularly in the presence of large cracks (>5 mm), the fatigue crack growth resistance and fracture toughness of
the Ti-6Al-4V material is superior when compared to both β-Cez conditions. However, for small crack sizes, the conditions of both the alloys under study show equivalent resistance
against fatigue crack growth. For the β-Cez material, where microstructures were optimized for high fracture toughness (conventional large crack sizes) by thermomechanical
processing, maximum K
Ic-values of 68 MPa√m of the β-processed β-Cez condition (tested in the longitudinal direction) decreased by ∼50 pct in the presence of small cracks (1 mm). A similar
decrease in fracture toughness was obtained by loading the β-processed β-Cez condition perpendicular to the flat surfaces of the pancake-shaped β grain structure (tested in the short transverse direction). These results were discussed in terms of the effectiveness of
the crack front geometry in hindering crack propagation. Further, the results of this study were considered for alloy selection
and optimized microstructures for fatigue and fracture critical applications. Finally, the advantage of the α+β-processed β-Cez condition in highly stressed engineering components is pointed out because of its overall superior combination of fatigue
crack initiation and propagation resistance (especially against small fatigue cracks). 相似文献
6.
Low-cycle fatigue behavior of INCONEL 718 superalloy with different concentrations of boron at room temperature 总被引:1,自引:0,他引:1
L. Xiao M. C. Chaturvedi D. L. Chen 《Metallurgical and Materials Transactions A》2005,36(10):2671-2684
Symmetrical push-pull low-cycle fatigue (LCF) tests were performed on INCONEL 718 superalloy containing 12, 29, 60, and 100
ppm boron (B) at room temperature (RT). The results showed that all four of these alloys experienced a relatively short period
of initial cyclic hardening, followed by a regime of softening to fracture at higher cyclic strain amplitudes (Δɛ
t
/2≥0.8 pct). As the cyclic strain amplitude decreased to Δɛ
t
/2≤0.6 pct, a continuous cyclic softening occurred without the initial cyclic hardening, and a nearly stable cyclic stress
amplitude was observed at Δɛ
t
/2=0.4 pct. At the same total cyclic strain amplitude, the cyclic saturation stress amplitude among the four alloys was highest
in the alloy with 60 ppm B and lowest in the alloy with 29 ppm B. The fatigue lifetime of the alloy at RT was found to be
enhanced by an increase in B concentration from 12 to 29 ppm. However, the improvement in fatigue lifetime was moderate when
the B concentration exceeded 29 ppm B. A linear relationship between the fatigue life and cyclic total strain amplitude was
observed, while a “two-slope” relationship between the fatigue life and cyclic plastic strain amplitude was observed with
an inflection point at about Δɛ
p
/2=0.40 pct. The fractographic analyses suggested that fatigue cracks initiated from specimen surfaces, and transgranular
fracture, with well-developed fatigue striations, was the predominant fracture mode. The number of secondary cracks was higher
in the alloys with 12 and 100 ppm B than in the alloys with 29 and 60 ppm B. Transmission electron microscopy (TEM) examination
revealed that typical deformation microstructures consisted of a regularly spaced array of planar deformation bands on {111}
slip planes in all four alloys. Plastic deformation was observed to be concentrated in localized regions in the fatigued alloy
with 12 ppm B. In all of the alloys, γ″ precipitate particles were observed to be sheared, and continued cyclic deformation reduced their size. The observed cyclic
deformation softening was associated with the reduction in the size of γ″ precipitate particles. The effect of B concentration on the cyclic deformation mechanism and fatigue lifetime of IN 718 was
discussed. 相似文献
7.
J. J. Kruzic J. H. Schneibel R. O. Ritchie 《Metallurgical and Materials Transactions A》2005,36(9):2393-2402
Ambient- to elevated-temperature fracture and fatigue-crack growth results are presented for five Mo-Mo3Si-Mo5SiB2-containing α-Mo matrix (17 to 49 vol pct) alloys, which are compared to results for intermetallic-matrix alloys with similar compositions.
By increasing the α-Mo volume fraction, ductility, or microstructural coarseness, or by using a continuous α-Mo matrix, it was found that improved fracture and fatigue properties are achieved by promoting the active toughening mechanisms,
specifically crack trapping and crack bridging by the α-Mo phase. Crack-initiation fracture toughness values increased from 5 to 12 MPa√m with increasing α-Mo content from 17 to 49 vol pct, and fracture toughness values rose with crack extension, ranging from 8.5 to 21 MPa√m at
ambient temperatures. Fatigue thresholds benefited similarly from more α-Mo phase, and the fracture and fatigue resistance was improved for all alloys tested at 1300 °C, the latter effects being
attributed to improved ductility of the α-Mo phase at elevated temperatures. 相似文献
8.
A method has been developed to produce grain sizes as small as 5 μm in alloys of β-CuAlNi. The alloys were of eutectoid composition
and a procedure was developed for determining the composition of a eutectoid alloy having any required value for transition
temperature (M
s
). The thermo-mechanical treatment involved two sequential stages of warm rolling followed by recrystallization. The alloys
produced were single phase β-type with no second phase being present. Characteristic two-stage stress-strain curves were obtained
for most of the specimens. It was generally found that the tensile strength and strain to failure increased with decreasing
grain size according to a Hall-Petch type relationship down to a grain size of 5 μm. A fracture strength of 1200 MPa and a
fracture strain of 10 pct were obtained in the best alloy. It was found that the major recovery mode, whether pseudoelastic
or strain-memory, did not have any significant effect on the total recovery obtained. Recovery properties were not affected
significantly by decreasing grain size, and 86 pct recovery could still be obtained at a grain size of around 10 μm. Grain
refinement improved the fatigue life considerably, possibly due to the high ultimate fracture stress and ductile fracture
mode. A fatigue life of 275,000 cycles could be obtained for an applied stress of 330 MPa and a steady state strain of 0.7
pct. At fine-grain sizes most of the fractures were due to transgranular-type brittle fracture and micro void-type ductile
fracture, depending on the alloy composition. It was suggested that the difference between the alloys was due to differences
in oxygen segregation at the grain boundaries. 相似文献
9.
Yi He Ph.D. Ke Yang Kai Liu Ph.D. Wei Sha Zhanli Guo 《Metallurgical and Materials Transactions A》2006,37(4):1107-1116
The age hardening kinetics in the temperature range of 713 to 813 K of a 2400 MPa grade cobalt-free maraging steel (Fe-(18.8
∼ 19.1) pct Ni-(4.4 ∼ 5.4) pct Mo-2.6 pct Ti, wt pct) has been studied. Study of microstructure and mechanical properties
showed that a high number of Ni3Ti and Fe2(Mo,Ti) precipitates were formed during the ageing process, which resulted in high strength and relatively low fracture toughness.
Ni3Ti was the main precipitation phase. Fractography has shown ductile failure of tensile and fracture toughness specimens. Thermodynamic
calculations showed that the equilibrium phases are Ni3Ti, Fe2(Mo,Ti), ferrite, and austenite. 相似文献
10.
A comparative study has been made of the room- and elevated-temperature properties, room-temperature fracture toughness, fatigue-crack
propagation rates, and 650 °C creep properties of Ti-24Al-14Nb-3V-0.5Mo with and without 0.9 at. pct Si. Both alloys have
microstructures consisting of the α
2, B2, and the orthorhombic O phase, with different proportions of the α
2 phase relative to the (O + B2) mixtures, depending on solution-treatment temperature. The alloy with a Si addition contains
additional primary ζ-Ti5Si3 particles distributed in the (O + B2) matrix. Tests of mechanical properties showed that the incorporation of a small fraction
(about 0.03 by volume) of the Ti5Si3 phase leads to greater room-temperature and elevated-temperature strengths, but lower room-temperature elongations and fracture
toughness as compared with the base alloy. Alloys containing greater volume fractions of the α
2 phase exhibited better tensile ductility, and this was attributed to the concurrent stabilization of the B2 phase. Examination
of tensile-tested and fatigued specimens indicates that the primary failure mode of the alloys, regardless of Si addition,
was due to the brittleness of the α
2 phase; the silicide particles that debonded from the matrix also contribute to cracking in the monotonic loading mode. Up
to a 20 pct improvement in creep-rupture life was observed in the Si-containing alloys, and this was interpreted in terms
of the solute-strengthening effect of Si. While the incorporated Ti5Si3 phase has an unfavorable effect on ductility and room-temperature fracture toughness, the difference in fatigue-crack propagation
rates between the alloys with and without Si is minimal. It is concluded that the controlling factor for the fatigue failure
in orthorhombic alloys is related to the (α
2 + O + B2) microstructure, instead of the Ti5Si3 particles. 相似文献
11.
A. Inoue S. Furukawa M. Hagiwara T. Masumoto 《Metallurgical and Materials Transactions A》1987,18(5):621-628
Ni-based amorphous wires with good bending ductility have been prepared for Ni75Si8B17 and Ni78P12B10 alloys containing 1 to 2 at. pct Al or Zr by melt spinning in rotating water. The enhancement of the wire-formation tendency
by the addition of Al has been clarified to be due to the increase in the stability of the melt jet through the formation
of a thin A12O3 film on the outer surface. The maximum wire diameter is about 190 to 200 μm for the Ni-Si (or P)-B-Al alloys and increases
to about 250 μm for the Ni-Si-B-Al-Cr alloys containing 4 to 6 at. pct Cr. The tensile fracture strength and fracture elongation
are 2730 MPa and 2.9 pct for (Ni0.75Si0.08B0.17
99Al1) wire and 2170 MPa and 2.4 pct for (Ni0.78P0.12B0.1)99Al1 wire. These wires exhibit a fatigue limit under dynamic bending strain in air with a relative humidity of 65 pct; this limit
is 0.50 pct for a Ni-Si-B-Al wire, which is higher by 0.15 pct than that of a Fe75Si10B15 amorphous wire. Furthermore, the Ni-base wires do not fracture during a 180-deg bending even for a sample annealed at temperatures
just below the crystallization temperature, in sharp contrast to high embrittlement tendency for Fe-base amorphous alloys.
Thus, the Ni-based amorphous wires have been shown to be an attractive material similar to Fe- and Co-based amorphous wires
because of its high static and dynamic strength, high ductility, high stability to thermal embrittlement, and good corrosion
resistance. 相似文献
12.
The influence of microstructure on the fracture toughness of Ti-23A1-9Nb-2Mo-1Zr-1.2Si (at. pct) and Ti-23A1-11Nb-0.9Si (at.
pct) Ti3Al-based alloys has been investigated. Basket-weave microstructures comprising different volume fractions of α
2 and retained β phases were produced by systematic heat treatments. Besides the volume fraction of the retained β phase, the average size of the β laths has also been used to characterize these microstructures. The toughness of both alloys was examined at room temperature,
and the brittle transgranular fracture modes were found to be controlled by microstructure. However, the toughness is not
determined solely by the volume fraction of the retained β phase, and a linear relationship has been obtained between the fracture toughness and the average size of the retained β laths. It appears therefore that the toughness of Ti3Al-based alloys at room temperature is controlled primarily by the width of retained β laths rather than by the retained β volume fraction. 相似文献
13.
Microstructure evolution in tial alloys with b additions: Conventional solidification 总被引:10,自引:0,他引:10
M. E. Hyman C. McCullough J. J. Valencia C. G. Levi R. Mehrabian 《Metallurgical and Materials Transactions A》1989,20(9):1847-1859
Solidification microstructures of arc-melted, near-equiatomic TiAl alloys containing boron additions are analyzed and compared
with those of binary Ti-Al and Ti-B alloys processed in a similar fashion. With the exception of the boride phase, the matrix
of the ternary alloy consists of the same α2 (DO19) and γ (Ll0) intermetallic phases found in the binary Ti-50 at. pct Al alloy. On the other hand, the boride phase, which is TiB (B27)
in the binary Ti-B alloys, changes to TiB2 (C32) with the addition of Al. The solidification path of the ternary alloys starts with the formation of primary α (A3)
for an alloy lean in boron (∼1 at. pct) and with primary TiB2 for a higher boron concentration (∼5 at. pct). In both cases, the system follows the liquidus surface down to a monovariant
line, where both α and TiB2 are solidified concurrently. In the final stage, the α phase gives way to γ, presumably by a peritectic-type reaction similar
to the one in the binary Ti-Al system. Upon cooling, the α dendrites order to α2 and later decompose to a lath structure consisting of alternating layers of γ and α2. 相似文献
14.
W. O. Soboyejo J. Dipasquale F. Ye C. Mercer T. S. Srivatsan D. G. Konitzer 《Metallurgical and Materials Transactions A》1999,30(4):1025-1038
This article presents the results of a study of the fatigue and fracture behavior of a damage-tolerant Nb-12Al-44Ti-1.5Mo
alloy. This partially ordered B2 + orthorhombic intermetallic alloy is shown to have attractive combinations of room-temperature
ductility (11 to 14 pct), fracture toughness (60 to 92 MPa√m), and comparable fatigue crack growth resistance to IN718, Ti-6Al-4V,
and pure Nb at room temperature. The studies show that tensile deformation in the Nb-12Al-44Ti-1.5Mo alloy involves localized
plastic deformation (microplasticity via slip-band formation) which initiates at stress levels that are significantly below the uniaxial yield stress (∼9.6 pct of
the 0.2 pct offset yield strength (YS)). The onset of bulk yielding is shown to correspond to the spread of microplasticity
completely across the gage sections of the tensile specimen. Fatigue crack initiation is also postulated to occur by the accumulation
of microplasticity (coarsening of slip bands). Subsequent fatigue crack growth then occurs by the “unzipping” of cracks along
slip bands that form ahead of the dominant crack tip. The proposed mechanism of fatigue crack growth is analogous to the unzipping
crack growth mechanism that was suggested originally by Neumann for crack growth in single-crystal copper. Slower near-threshold
fatigue crack growth rates at 750 °C are attributed to the shielding effects of oxide-induced crack closure. The fatigue and
fracture behavior are also compared to those of pure Nb and emerging high-temperature niobium-based intermetallics. 相似文献
15.
Room temperature tension-tension fatigue tests were performed on two lamellar γ/γ′-δ alloys, one with 0 pct Cr and one with
6 pct Cr. The 6 pct Cr alloy was solidified at 3 cmJh while the 0 pct Cr alloy was solidified at 3 cm/h and 5.7 cm/h. Fatigue
testing was done on both alloys in the as-directionally solidified condition and on the 0 pct Cr alloy after heat treatment.
Increasing the growth speed of the 0 pct Cr alloy increased the fatigue life of the material at stresses above the 107 cycle fatigue limit. Partial solution treating and aging of the 0 pct Cr alloy,R = 3 cm/h, increased the fatigue life relative to the as-directionally solidified material at high stresses, to the same extent
as increasing the growth speed. Full solution treatment and aging of the 0 pct Cr alloy,R = 5.7 cm/ h, caused a reduction in the fatigue life relative to the as-directionally solidified material. Fatigue cracking
tended to be faceted in the 6 pct Cr alloy as opposed to the more ductile failure of the 0 pct Cr alloy. Microstructural perfection,
grain size and shape, interlamellar spacing, longitudinal cracking, and longitudinal and transverse ductility all are believed
to have influenced the fatigue resistance of the alloys. 相似文献
16.
The influence of Mn content on the ductile-brittle transition in 16 to 36 wt pct Mn steels was investigated and interpreted
in light of the evolving microstructure. It was found that when hcp ε martensite is present in the as-quenched condition or
forms during deformation, it lowers the toughness. In 25Mn steel, the stress concentrations at e plate intersections result
in the formation of planar void sheets along the {111}γ planes. The deformation-induced α’ martensite in 16 to 20 pct Mn alloys enhances the toughness, but leads to a ductile-to-brittle
transition at low temperatures that is due to the intrusion of an intergranular fracture mode. Binary alloys with greater
than 31 pct Mn also fracture in an intergranular mode at 77 K although the impact energy remains quite high. Auger spectroscopy
of the fracture surfaces shows no evidence of significant impurity segregation, which suggests the importance of slip heterogeneity
in controlling intergranular fracture in these alloys. 相似文献
17.
A metallographic study of the porosity and fracture behavior in unidirectionally solidified end chill castings of 319.2 aluminum
alloy (Al-6.2 pct Si-3.8 pct Cu-0.5 pct Fe-0.14 pct Mn-0.06 pct Mg-0.073 pct Ti) was carried out using optical microscopy
and scanning electron microscopy (SEM) to determine their relationship with the tensile properties. The parameters varied
in the production of these castings were the hydrogen (∼0.1 and ∼0.37 mL/100 g Al), modifier (0 and 300 ppm Sr), and grain
refiner (0 and 0.02 wt pct Ti) concentrations, as well as the solidification time, which increased with increasing distance
from the end chill bottom of the casting, giving dendrite arm spacings (DASs) ranging from ∼15 to ∼95 /im. Image analysis
and energy dispersive X-ray (EDX) analysis were employed for quantification of porosity/microstructural constituents and fracture
surface analysis (phase identification), respectively. The results showed that the local solidification time(viz. DAS) significantly influences the ductility at low hydrogen levels; at higher levels, however, hydro-gen has a more pronounced
effect (porosity related) on the drop in ductility. Porosity is mainly observed in the form of elongated pores along the grain
boundaries, with Sr increasing the porosity volume percent and grain refining increasing the probability for pore branching.
The beneficial effect of Sr modification, however, improves the alloy ductility. Fracture of the Si, β-Al5FeSi, α- Al15(Fe,Mn)3Si2, and Al2Cu phases takes place within the phase particles rather than at the particle/Al matrix interface. Sensitivity of tensile properties
to DAS allows for the use of the latter as an indicator of the expected properties of the alloy. 相似文献
18.
19.
J. Robles K. R. Anderson J. R. Groza J. C. Gibeling 《Metallurgical and Materials Transactions A》1994,25(10):2235-2245
The cyclic deformation behavior of a dispersion-strengthened copper alloy, GlidCop Al-15, has been studied at plastic strain
amplitudes in the range 0.1 pct ≤Δε
p/2 ≤ 0.8 pct. Compared to pure polycrystalline copper, the dispersion-strengthened material exhibits a relatively stable cyclic
response as a consequence of the dislocation substructures inherited from prior processing and stabilized by the A12O3 particles. These dislocation structures remain largely unaltered during the course of deformation; hence, they do not reveal
any of the features classically associated with copper tested in fatigue. At low amplitudes, the fatigue lifetimes of the
dispersion-strengthened copper and the base alloy are similar; however, the former is more susceptible to cracking at stress
concentrations because of its substantially greater strength. This similarity in fatigue lifetimes is a consequence of the
dispersal of both deformation and damage accumulation by the fine grain size and dislocation/particle interactions in the
GlidCop alloy. The operation of these mechanisms is reflected in the fine surface slip markings and rough fracture surface
features for this material.
Formerly Graduate Research Assistant, University of California, Davis, CA 相似文献
20.
Sug-Woo Jung Suk-Joong L. Kang Sunghak Lee Eun-Pyokim Joon-Woong Noh Woon-Hyung Baek 《Metallurgical and Materials Transactions A》2002,33(4):1213-1219
A carburization technique using a Cr powder layer has been developed to control the diffusion depth of carbon in W-Ni-Fe heavy
alloys. The aged heavy alloy samples were covered with a Cr powder layer of about 1-mm thickness and then packed with carbon
black powder. The packed samples were heat-treated at 1150 °C for 10 minutes in H2 and then for 50 minutes in N2. The carburization treatment resulted in the formation of Cr7C3 and Fe3W3C around the tungsten grains from the sample surface with a thickness of 40 to 50 μm. This carburized layer was much thinner than that formed without a Cr powder layer under the same experimental conditions.
With the surface carburization, the surface hardness increased by ∼75 pct, from 508 to 888 VHN, and the impact energy decreased
by ∼31 pct, from 123 to 85 J. After the carburization treatment, the main fracture behavior in a dynamic torsional test changed
from smearing of the matrix to cleavage of the tungsten grains. A high-speed impact test showed that the surface carburization
of penetrators induced the formation of many cracks around the penetrator surface, enhanced the self-sharpening, and improved
the penetration performance. It appears that the developed technique provides an easy method of carburization without serious
deterioration of the toughness of the material. 相似文献