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1.
《粉末冶金学》2013,56(29):55-66
AbstractA study of the sintering behaviour of iron compacts containing additions of tin up to 1 wt.-% has been made. A tensile strength of 234 MN/m2 (34 x 103 lbf/in2) has been achieved with an optimum tin addition of 0·5 wt.-%, sintering being carried out for 10 min at 1100°C (1373 K) in a reactive halide atmosphere. Combination of the two ‘activating’ techniques (addition of tin and sintering in a reactive atmosphere) permits current properties to be attained at considerably lower sintering temperatures or sintered densities, and is much more effective than when they are applied individually. A tensile strength of 165·3 MN/m2 (24 x 103lbf/in2), achieved by sintering at 1200°C (1473 K) for 10 min with an addition of 0·5 wt.-% tin can be obtained by reactive-sintering the same composition at 900°C (1173 K) for 10 min. Alternatively, the density of the part can be reduced from 6·7 to 6·2 g/cm3 with no loss of strength or elongation. Tin in excess of 0·5 wt.-% causes deterioration in properties under the sintering conditions studied and a reason for this is cited. The improvements in properties are lost also if admixed lubricant is used in the compactionprocess. 相似文献
2.
T. D. Bayha R. J. Kilmer F. E. Wawner 《Metallurgical and Materials Transactions A》1992,23(6):1653-1662
A fracture mechanics approach was used to determine the plane strain fracture toughness (K
IC) of a mechanically alloyed Al-9Ti 20 vol pct cobalt sol-gel-coated SiC particle-reinforced composite. Processing defects
consisting of clumped SiC particulate, bonded by the sol-gel, initiated failure in tensile tests. The defects were measured
and the fracture toughness was calculated using the Irwin relation. The value ofK
IC for the as-received material was determined to be equal to 4.7 MPa·m1/2 at room temperature. Annealing the material for 120 hours and 400 hours at 500 °C increased the fracture toughness. This
can be attributed to coarsening of an Al3Ti strengthening phase. Tensile tests conducted at 200 °C show thatK
IC decreases at that temperature for each annealing condition. The sensitivity to the presence of the defects is greatest for
samples annealed at 500 °C for 120 hours. The effect of the defects on the failure mechanism of the composite material as
a function of temperature was determined. At room temperature, the Co/SiC processing defects provide low-energy paths for
crack propagation; at 500 °C, the defects serve as void nucleation sites. 相似文献
3.
Massive electrodeposits of nickel and Ni?Co alloys ranging up to 43 pct Co were examined microstructurally and tested to determine tensile properties and static and dynamic fracture toughness. Specimens were also tested after being annealed at 575 K. Annealing increased grain size, decreased yield, and ultimate strengths, and increased ductility and dynamic toughness. The as-plated Ni-43 Co was the only material to exhibit validK IC values, averaging about 38 MN/m3/2. In instrumented dynamic tests on precracked Charpy bars, the same material exhibited aK Id of 50 MN/m3/2. The yield strength of the Ni-43 Co alloy was 1154 MN/m2. All the materials tested showed dimpled, ductile rupture fracture surfaces. The Hall-Petch behavior of the nickel indicated that it is much easier to initiate flow in normal grain boundary structures than in structures composed of dislocation cell walls. 相似文献
4.
Riming Wu Wei Li Shu Zhou Yong Zhong Li Wang Xuejun Jin 《Metallurgical and Materials Transactions A》2014,45(4):1892-1902
Fracture toughness K IC was measured by double edge-notched tension (DENT) specimens with fatigue precracks on quenching and partitioning (Q&P)-treated high-strength (ultimate tensile strength [UTS] superior to 1200 MPa) sheet steels consisting of 4 to 10 vol pct of retained austenite. Crack extension force, G IC, evaluated from the measured K IC, is used to analyze the role of retained austenite in different fracture behavior. Meanwhile, G IC is deduced by a constructed model based on energy absorption by martensite transformation (MT) behavior of retained austenite in Q&P-treated steels. The tendency of the change of two results is in good agreement. The Q&P-treated steel, quenched at 573 K (300 °C), then partitioned at 573 K (300 °C), holding for 60 seconds, has a fracture toughness of 74.1 MPa·m1/2, which is 32 pct higher than quenching and tempering steel (55.9 MPa·m1/2), and 16 pct higher than quenching and austempering (QAT) steel (63.8 MPa·m1/2). MT is found to occur preferentially at the tips of extension cracks on less stable retained austenite, which further improves the toughness of Q&P steels; on the contrary, the MT that occurs at more stable retained austenite has a detrimental effect on toughness. 相似文献
5.
《粉末冶金学》2013,56(27):22-38
AbstractThe difficulties encountered in the measurement of the toughness of cemented tungsten carbides are discussed and the benefits that might be expected from an application of fracture mechanics to the problem are described. A simple method for the measurement of the fracture-toughness parameter, KIC, for the more brittle grades of carbide is considered. The method involves indenting a beam-shaped specimen with a Knoop diamond to produce a crack, and loading the pre-cracked specimen to failure in four-point bending. Results from two grades of cemented carbide are presented and show that a standard error of the mean KIC of ~3% can be obtained from a set of 10 measurements, with a minimum of specimen preparation and no special testing equipment. The results show also that the toughness of the cemented carbide can be affected by grain-size variations within the same batch of material and by the pressing direction during manufacture. 相似文献
6.
Effect of hot-rolling reduction on shape of sulfide inclusions and fracture toughness of AISI 4340 ultrahigh strength steel 总被引:1,自引:0,他引:1
Yoshiyuki Tomita 《Metallurgical and Materials Transactions A》1988,19(6):1555-1561
Commercial AISI 4340 ultrahigh strength steels with hot-rolling reductions of 80 to 98 pct have been studied to determine
the effect of the shape of sulfide inclusions on plane-strain fracture toughness(K
IC
) of the ultrahigh strength low alloy steels. The significant conclusions are as follows: decreasing the hot-rolling reduction
from 98 to 80 pct for the steels modified the shape of sulfide inclusions from the stringer (average aspect ratio = 17.5)
to the ellipse (average aspect ratio = 3.8). This improved theK
IC
in the longitudinal testing orientation by about 20 MPa · m1/2 at similar strength levels. This could be due to the fact that the ellipsed sulfide-inclusions separate from the matrix during
plastic deformation, producing large voids. During testing these act to blunt and arrest cracks propagating across the specimen
which would normally cause failure. The decrease in the hot-rolling reduction also developed theK
IC
in the transverse testing orientation by about 17 MPa · m1/2 at increased ductility and Charpy impact energy levels. This can be attributed to the fact that lamellate fracture, which
occurs in a brittle manner along the interfaces of the sulfide-inclusion/matrix at the crack tip, is considerably suppressed
by modifying the shape of the inclusions from the stringer to the ellipse. 相似文献
7.
The fracture behavior of 52100 steel hardened and tempered to RC62 has been investigated as a function of austenitizing over the temperature range from 800 to 1100°C. Specimens were homogenized
at 1150°C and either furnace cooled or isothermally transformed at 580°C to produce a pearlitic microstructure prior to austenitizing
for hardening. Furnace-cooled specimens developed a proeutectoid carbide network that did not dissolve during subsequent austenitizing
below Acm
. The residual proeutectoid carbides and the carbide-free martensite-austenite structure between them controlled fracture and
produced KIC of 19 MPa \ m1/2, the highest determined in this investigation. The specimens isothermally transformed prior to austenitizing below Acm produced a microstructure of fine spherical carbides dispersed throughout a fine martensitic matrix and did not contain residual
proeutectoid carbides. The transgranular fracture of the latter specimens by microvoid coalescence around the closely spaced
spherical carbides resulted in the lowest values of fracture toughness, 14 to 16 MPa\ m1/2, determined in these experiments. Austenitizing above Acm caused solution of all carbides, a gradual coarsening of the austenitic grain size, a transition to plate martensite, and
an increase in retained austenite. Fracture toughness increased slightly with increasing austenitizing temperature above Acm despite the fact that fracture propagated primarily along the austenitic grain boundaries. The improved fracture toughness,
verified by scanning electron microscopy of the fatigue crack-overload fracture interface, is believed to be caused in part
by transgranular crack propagation during the first stages of crack extension that are most important in determining K1C. 相似文献
8.
The diffusivity and solubility of oxygen in liquid tin and solid silver in the temperature range of about 750° to 950°C (1023
to 1223 K) and the diffusivity of oxygen in solid nickel at 1393°C (1666 K) were determined using the electrochemical cell
arrangement of cylindrical geometry: Liquid or Solid Metal + O (dissolved) | ZrO2 + (3 to 4%)CaO | Pt, air The diffusivity and solubility of oxygen in liquid tin are given by:D
O(Sn) = 9.9 × 10−4 exp(−6300/RT) cm2/s (9.9 × 10−8 exp − 6300/RT m2/s) andN
O
S
(Sn) = 1.3 × 105 exp(−30,000/RT) at. pct The diffusivity and solubility of oxygen in solid silver follow the relations:D
O(Ag) = 4.9 × 10−3 exp (−11,600/RT) cm2/s ( 4.9 × 10−7 exp − 11,600/RT m2/s) andN
O
S
(Ag) = 7.2 exp (−11,500/RT) at. pct The experimental value for the preexponential in the expression forD
O(Ag) is lower than the value calculated according to Zener’s theory of interstitial diffusion by a factor of 11. The diffusivity
of oxygen in solid nickel at 1393°C (1666 K) was found to be 1.3 × 10−6 cm2/s (1.3 × 10−10 m2/s).
Formerly Graduate Student, Department
Formerly Graduate Student, Department
Formerly Graduate Student, Department
This paper is based upon a
This paper is based upon a
This paper is based upon a
This paper is based upon a 相似文献
9.
The high cycle fatigue (HCF) behavior of the oxide dispersion strengthened (ODS) MA 754 alloy has been determined as a function
of specimen orientation. The fatigue life showed anisotropic behavior with the longest and shortest lives in the longitudinal
and short transverse directions, respectively. Surface porosity, due to oxidation, was found to affect fatigue life in the
long transverse orientation more than in the longitudinal orientation. The fatigue crack growth behavior in MA 754 exhibited
a directional dependence. In general, the crack growth rates in the longitudinal direction were lower than those in the long
transverse direction. The ΔK
th
was ∼11 MN ·-3/2 and 9 MN · m-3/2 for the longitudinal and the long transverse orientation, respectively. This behavior was explained on the basis of the unusual
grain structure and the texture exhibited by this alloy as well as different crack closure effects. It was found that a consideration
based on the crack growth rates results, obtained from fracture mechanics specimens, could not explain the anisotropic behavior
of the HCF properties of MA 754. However, the anisotropic HCF properties could be rationalized on the basis of the differences
in the modes of crack initiation. 相似文献
10.
E. L. Brown T. A. Whipple R. L. Tobler 《Metallurgical and Materials Transactions A》1983,14(5):1179-1188
The first fracture toughness measurements for CF8 stainless steel castings in liquid helium at 4 K are reported. Single-phase (austenite) and duplex (austenite + δ-ferrite) castings were tested. On the basis of estimates from J-integral data, the plane-strain fracture toughness (Klc) of castings containing 3.2 to 14.5 pct δ-ferrite ranged from 84 to 179 MPa · ml/2 at 4 K. In contrast, a fully austenitic casting (0 pct δ-ferrite) exhibited a Klc, value of 331 MPa · ml/2, which is nearly equivalent to the toughness of a wrought AISI 304 stainless steel of a similar strength. Light and scanning electron microscopy studies indicate that the inferior toughness of castings containing δ-ferrite may be attributed to the brittleness of this body-centered-cubic phase at cryogenic temperatures and its distribution in the microstructure. The relative stability of the austenitic phase with respect to martensitic phase transformation may also play a significant role. 相似文献
11.
E. L. Brown T. A. Whipple R. L. Tobler 《Metallurgical and Materials Transactions A》1983,14(6):1179-1188
The first fracture toughness measurements for CF8 stainless steel castings in liquid helium at 4 K are reported. Single-phase (austenite) and duplex (austenite + δ-ferrite) castings were tested. On the basis of estimates from .J-integral data, the plane-strain fracture toughness(K lc) of castings containing 3.2 to 14.5 pct δ-ferrite ranged from 84 to 179 MPa · m1/2 at 4 K. In contrast, a fully austenitic casting (0 pct (δ-ferrite) exhibited aK lc value of 331 MPa · m-2, which is nearly equivalent to the toughness of a wrought AISI 304 stainless steel of a similar strength. Light and scanning electron microscopy studies indicate that the inferior toughness of castings containing ·-ferrite may be attributed to the brittleness of this body-centered-cubic phase at cryogenic temperatures and its distribution in the microstructure. The relative stability of the austenitic phase with respect to martensitic phase transformation may also play a significant role. 相似文献
12.
W. W. Gerberich H. Huang W. Zielinski P. G. Marsh 《Metallurgical and Materials Transactions A》1993,24(3):535-543
An interconnected set of observations assesses current equilibrium models of the ductile-brittle-transition temperature (DBTT).
This involvesin situ transmission electron microscopy (TEM) studies of crack-tip dislocations in single and polycrystals and bulk fracture toughness
tests at various temperatures. Beyond KI values of 8 MPa · m1/2 in both iron-base single and polycrystals, large numbers of redundant dislocations are created, as postulated recently by
Weertman. [38] Still, the necessary shielding dislocations, as required by equilibrium, can be detected at values as high
as 20 and 40 MPa · m1/2 byex situ TEM and electron channeling, respectively. In addition, the close approach of dislocations to the crack tip in some of the
studies, as opposed to others, suggests that large dislocation free zones (DFZ) are a thin-film artifact. However, a failure
criterion based partly on the Rice-Thomson model’21 is both consistent with the absence of a large DFZ and observed fracture
toughness variations with test temperature. It is emphasized that this toughness transition is entirely in the semibrittle
regime where cleavage is the failure mode. Nevertheless,K
lc values increase from 3 to 60 MPa·m1/2 with an increase in test temperature.
This article is based on a presentation made in the symposium “Quasi-Brittle Fracture” presented during the TMS fall meeting,
Cincinnati, OH, October 21–24, 1991, under the auspices of the TMS Mechanical Metallurgy Committee and the ASM/MSD Flow and
Fracture Committee. 相似文献
13.
《粉末冶金学》2013,56(30):130-152
AbstractLaboratory compaction and ejection studies have been made using a reduced iron powder mixed with a number of zinc stearates having median particle sizes between 4 and 22μm. Comparable experiments were carried out on a fully instrumented production press, which was operated at compacting pressures between 300 and 500 MN/m2 to produce compacts with true densities ranging from 5·90 to 6·70 g/cm3. Determination of ejection forces by the two methods enabled calculations of the coefficients of friction between compact and die wall to be made for mixtures containing 0·5–2·0 wt.% zinc stearate. These showed that the behaviour during compaction and ejection was comparable on both laboratory and production scales and gave very similar results. An interpretation of the results is given and values of coefficients of friction are presented which show that these are dependent on the type of zinc stearate used. 相似文献
14.
The plane strain fracture toughness values,K
Ic
, the fatigue crack growth rates and the tensile properties of M-50 and 18-4-1 high speed steels have been measured as a function
of tempering temperature. The M-50 was a vacuum arc remelted grade (VIM-VAR) and the 18-4-1 an electroslag grade, and both
are used in mainshaft gas turbine bearings. At the usual hardness for bearings, Rockwell C 62, 18-4-1 exhibited a slightly
higher fracture toughness (21 MPa·m1/2) than M-50 (18 MPa·m1/2). The fatigue crack growth rates were very similar, and in the slow growth region followed the usual power law,dC/dN=(ΔK)
m
withm=3 to 4. The crack propagation rates were still significant at values as low as ΔK=5 MPa·m1/2. SEM studies of the fracture surfaces showed complex transgranular fracture paths for both steels. The tensile strengths
and the elongations of M-50 were somewhat higher than the corresponding values for 18-4-1 but the yield strengths of the two
steels were similar. The microstructures of these steels were markedly different, with M-50 exhibiting 2.6 vol pct undissolved
carbides and the 18-4-1 showing 15.2 vol pct carbides, but the fatigue and fracture behaviors were similar. 相似文献
15.
The tensile properties, fracture toughness and stress corrosion cracking (SCC) behavior of HY-180 M steel at 22 °C were studied
after final 5 h overaging treatments >510 ≤650 °C. SCC tests were conducted for 1000 h with compact tension specimens in aqueous
3.5 pct NaCl solutions at a noble (anodic) potential of −0.28 VSHE ( −0.48 VAg/AgC1) and a cathodic protection potential of −0.80 VSHE (−1.0 VAg/AgC1). The SCC resistance improved at aging temperatures >565 °C, the most significant improvement being at −0.80 VShe, especially after 650 ° aging whereK
ISCC was raised to at least 110 MPa · m1/2. However, this was at the expense of mechanical properties. Provided low crack propagation rates of ∼3 X 10−11 m/s at −0.80V
SHEmay be tolerated, the best compromise between strength, toughness, and SCC resistance was obtained after 594 °C aging. Under
these conditions, stress intensities as high as ∼ 110 MPa · m1/2 can be used, with a yield strength of ∼ 1150 MPa and fracture toughness of ∼ 170 MPa · m1/2. The retained austenite content after aging increased with aging temperature up to 25 pct by vol at 650 °C. It appeared to
correlate with improved SCC resistance, but other microstructural effects associated with aging may be involved.
Formerly Research Associate with theDepartment of Metallurgical Engineering , University of BritishColumbia 相似文献
16.
《粉末冶金学》2013,56(23):193-208
AbstractThe creep behaviour of high-density silicon carbide has been examined under four-point transverse bending in air at temperatures from 1000 to 1300°C. Stresses in the range 0·207 GN m?2 (30 000 Ib in?2) to 0·496 GN m?2 (72000 lb in?2) were applied.In tests lasting up to 3·6 Msec (1000 h) the creep strain (?p) increased with time (t) as ?p = Atk where k was between 0·2 and 0·5. The dependence of A on stress (σ) and absolute temperature (T) was found to be with n between 1 and 2 and Q~230 kJ mole?1 (55 kcal mole?1).These results are compared with estimates of creep in SiC obtained by extrapolation of steady-state creep data from higher temperatures. 相似文献
17.
Felipe P. Calderon Nobuo Sano Yukio Matsushita 《Metallurgical and Materials Transactions B》1971,2(12):3325-3332
The measurement of the diffusivities of manganese and silicon in molten binary ferroalloys over the whole range of composition
was undertaken to clarify existing but conflicting data at lower concentrations, to present new data at higher concentrations
and to indirectly confirm the behavior of both systems observed in thermodynamic studies. The experiments were carried out
under argon atmosphere in a Tammann furnace. The diffusion couples were held in 5 mm ID alumina tubes (98 pct Al2O3). Electron probe microanalysis of the samples led to a diffusion-penetration curve for the system under consideration. Results
obtained over the whole range of composition showed a slight negative deviation for the Fe−Mn system and a very large positive
deviation for the Fe−Si system. At lower concentrations (0 to 4 pct Mn), the temperature dependence of managanese diffusivity
for the Fe−Mn binary alloy in the temperature range 1550° to 1700°C is as follows:D
Fe−Mn=1.8×10−3 exp (−13,000/RT) cm2/sec
The concentration dependence of manganese diffusivity for the same system at 1600°C may be expressed asD
Fe−Mn={5.48−0.0137 (%Mn)+0.000276 (%Mn)2}×10−5 cm2/sec
The temperature dependence of silicon diffusivity for the Fe−Si binary system in the temperature range 1550° to 1725°C at
various concentrations is as follows:D
Fe−Si=2.8×10−3 exp (−11,900/RT) cm2/sec at 20 pct SiD
Fe−Si=2.1×10−3 exp (−13,200/RT) cm2/sec at 12.5 pct SiD
Fe−Si=5.1×10−4 exp (−9,150/RT) cm2/sec at 2.2 pct Si
FELIPE P. CALDERON, formerly Graduate Student. University of Tokyo, Tokyo, Japan.
This paper is based on a portion of a thesis submitted by FELIPE P. CALDERON in partial fulfillment of the requirements for
the degree of Doctor of Engineering at University of Tokyo. 相似文献
18.
《粉末冶金学》2013,56(4):484-487
AbstractScanning electron microscopy and X-ray diffraction analysis were used to study microstructure and mechanical properties of PM Ni56Fe19Al25 alloy. The results indicate that as sintered specimen is (β+γ) dual phase structure, and its density is 6·54 g cm?3 (the relative density is 94·0%), tensile strength is 771 MPa and the total strain is 4·3%. As quenched specimen presents a large superelasticity with the maximum recovery strain of 4·5%, and its tensile strength is 850 MPa and the total strain is 9·2%. The fracture modes of Ni56Fe19Al25 alloy is transgranular, intergranular and tough mixed type. 相似文献
19.
O. N. Grigor'ev S. S. Dzhamarov V. I. Trefilov A. M. Shatokhin 《Powder Metallurgy and Metal Ceramics》1981,20(1):42-48
Conclusions An investigation was carried out into the effect of thermal cycling on the structural state of polycrystals based on the high-density boron nitride modifications. It is shown that a two-phase material is characterized by a high level of macro- and microstresses, which control its brittle rupture behavior and mechanical properties. In particular, microcracking processes initiated by internal stresses after the application of external load promote stress relaxation at the tip of a propagating macrocrack, thereby imparting high fracture toughness (Kc 16–18 MN/m3/2) to the material. During heat treatment (performed in this work at T 800°C) internal stress relaxation takes place, which is accompanied by a fall in fracture toughness to the level characteristic of unstressed single-phase sintering (Kc 10–14 MN/m3/2) and changes in hardness and rupturing stress.Translated from Poroshkovaya Metallurgiya, No. 1(217), pp. 53–61, January, 1981. 相似文献
20.
A. Moitra P. R. Sreenivasan S. L. Mannan V. Singh 《Metallurgical and Materials Transactions A》2005,36(11):2957-2965
The ductile-brittle transition temperature (DBTT) of 9Cr-1Mo steel was characterized by an RT
NDT-based K
IR
curve approach and a reference temperature (T
0)-based master curve (MC) approach. The MC was developed at a dynamic loading condition (loading rate of 5.12 m/s), using
precracked Charpy V-notch (PCVN) specimens, and the reference temperature was termed T
0
dy
. The RT
NDT and T
0
dy
were determined to be −25 °C and −52 °C, respectively. The T
0
dy
was also estimated from instrumented CVN tests, using a modified Schindler procedure to evaluate K
Jd
; the result shows close agreement with that obtained from the PCVN tests. The ASME K
IR
-curve approach proves to be too conservative compared to the obtained trend of the fracture toughness with temperature. The
cleavage fracture stress, σ*
f
, estimated from the critical length, l*, shows good agreement with that estimated from the load-temperature diagram (2400 to 2450 MPa), which was constructed from
the CVN test results. The crack initiation mechanism has been identified as decohesion of the particle-matrix interface, rather
than as the fracture of the particles. 相似文献