共查询到20条相似文献,搜索用时 31 毫秒
1.
J. S. Santner 《Metallurgical and Materials Transactions A》1981,12(10):1823-1826
The purpose of the present investigation is to determine the relative importance of minor variations in alloy chemistry and
thermomechanical treatment on the low cycle fatigue behavior of 7000 series aluminum alloys. Two types of alloying variations
are considered: changing the alloy purity level by controlling the iron and silicon content, and changing the grain refiner
from chromium to zirconium. The effects of these alloying variations, with regard to mechanical properties other than low
cycle fatigue, have been discussed elsewhere.1-4The purpose of thermomechanical processing is to provide increased strength over 7075-T7351 with equivalent fracture toughness
and corrosion properties.5-7 The effect of the dislocation substructure introduced by thermomechanical processing (TMP) on the high cycle fatigue behavior
of 7075 was documented by Reimann and Brisbane.8 The present work was undertaken to determine the relative importance of purity level, dispersoid type, and dislocation substructure
(TMP) on the low cycle fatigue behavior of 7000 series aluminum alloys.
formerly with the Air Force Materials Laboratory, Wright-Patterson AFB, OH 相似文献
2.
The effect of heat treatment on microstructure and cryogenic fracture properties in 5Ni and 9Ni steel 总被引:2,自引:0,他引:2
Heat treatments were utilized in 5Ni and 9Ni steel which resulted in the development of tempered microstructures which contained
either no measurable retained austenite (<0.5 pct) or approximately 4 to 5 pct retained austenite as determined by X-ray diffraction.
Microstructural observations coupled with the results of tensile testing indicated that the formation of retained austenite
correlated with a decrease in carbon content of the matrix. Relative values ofK
IC
at 77 K were estimated from slow bend precracked Charpy data using both the COD and equivalent energy measurements. In addition,
Charpy impact properties at 77 K were determined. In the 9Ni alloy, optimum fracture toughness was achieved in specimens which
contained retained austenite. This was attributed to changes in yield and work hardening behavior which accompanied the microstructural
changes. In the 5Ni alloy, fracture toughness equivalent to that observed in the 9Ni alloy was developed in grain refined
and tempered microstructures containing <0.5 pct retained austenite. A decrease in fracture toughness was observed in grain
refined 5Ni specimens containing 3.8 pct retained austenite due to the premature onset of unstable cracking. This was attributed
to the transformation of retained austenite to brittle martensite during deformation. It was concluded that the formation
of thermally stable retained austenite is beneficial to the fracture toughness of Ni steels at 77 K as a result of austenite
gettering carbon from the matrix during tempering. However, it was also concluded that the mechanical stability of the retained
austenite is critical in achieving a favorable enhancement of cryogenic fracture toughness properties.
Formerly with Union Carbide Corporation, Tarrytown, NY 相似文献
3.
Fe-12 Mn alloys undergo failure by catastrophic intergranular fracture when tested at low temperature in the as-austenitized
condition, a consideration which prevents their use for structural applications at cryogenic temperatures. The present research
was undertaken to identify modifications in alloy composition or heat treatment which would suppress this embrittlement. Chemical
and microstructural analyses were made on the prior austenite grain boundaries within the alloy in its embrittled state. These
studies failed to reveal a chemical or microstructural source for the brittleness, suggesting that intergranular brittleness
is inherent to the alloy in the as-austenitized condition. The addition of 0.002 to 0.01 wt pct boron successfully prevented
intergranular fracture, leading to a spectacular improvement in the low temperature impact toughness of the alloy. Autoradiographic
studies suggest that boron segregates to the austenite grain boundaries during annealing at temperatures near 1000 °C. The
cryogenic toughness of a Fe-12Mn-0.002B alloy could be further improved by suitable tempering treatments. However, the alloy
embrittled if inappropriate tempering temperatures were used. This temper embrittlement was concom-itant with the dissolution
of boron from the prior austenite grain boundaries, which reestablishes the intergranular fracture mode. 相似文献
4.
Z. Chen J. Huang R. F. Decker S. E. Lebeau L. R. Walker O. B. Cavin T. R. Watkins C. J. Boehlert 《Metallurgical and Materials Transactions A》2011,42(5):1386-1399
Tensile, fatigue, fracture toughness, and creep experiments were performed on a commercially available magnesium-aluminum
alloy (AM60) after three processing treatments: (1) as-THIXOMOLDED (as-molded), (2) THIXOMOLDED then thermomechanically processed
(TTMP), and (3) THIXOMOLDED then TTMP then annealed (annealed). The TTMP procedure resulted in a significantly reduced grain
size and a tensile yield strength greater than twice that of the as-molded material without a debit in elongation to failure
(ε
f
). The as-molded material exhibited the lowest strength, while the annealed material exhibited an intermediate strength but
the highest ε
f
(>1 pct). The TTMP and annealed materials exhibited fracture toughness values almost twice that of the as-molded material.
The as-molded material exhibited the lowest fatigue threshold values and the lowest fatigue resistance. The annealed material
exhibited the greatest fatigue resistance, and this was suggested to be related to its balance of tensile strength and ductility.
The fatigue lives of each material were similar at both room temperature (RT) and 423 K (150 °C). The tensile-creep behavior
was evaluated for applied stresses ranging between 20 and 75 MPa and temperatures between 373 and 473 K (100 and 200 °C).
During both the fatigue and creep experiments, cracking preferentially occurred at grain boundaries. Overall, the results
indicate that thermomechanical processing of AM60 dramatically improves the tensile, fracture toughness, and fatigue behavior,
making this alloy attractive for structural applications. The reduced creep resistance after thermomechanical processing offers
an opportunity for further research and development. 相似文献
5.
Z. W. Zhang C. T. Liu Y. R. Wen A. Hirata S. Guo G. Chen M. W. Chen Bryan A. Chin 《Metallurgical and Materials Transactions A》2012,43(1):351-359
This study investigated the effect of aging and thermomechanical treatments on the mechanical properties of a nanocluster-strengthened
ferritic steel, Fe-1.5Mn-2.5Cu-4.0Ni-1.0Al (wt pct). The effect of thermomechanical treatments on the microhardness and tensile
properties were measured at room temperature and correlated with microstructural features. Cu-rich precipitates were characterized
by transmission electron microscopy and were found to coarsen slowly during long-time aging. The microhardness measurements
indicate a typical precipitation hardening behavior during aging at 773 K (500 °C). Tensile tests showed that thermomechanical
treatments can improve the mechanical strength and ductility of the nanocluster-strengthened ferritic steel significantly
compared with those without the treatments. Fractography results indicated that the high yield strength resulted from precipitation
hardening makes the steel more susceptible to grain-boundary decohesion, which can be suppressed by grain refinement. Atmosphere
adsorption and diffusion along grain boundaries were found to intensify brittle intergranular fracture, and this embrittlement
can be avoided by vacuum heat treatment. 相似文献
6.
Joseph S. Santner 《Metallurgical and Materials Transactions A》1978,9(6):769-779
Ten different alloys based on the 7075 composition were used to study the effect of purity level, dispersoid type, and heat
treatment on fracture toughness. Five purity levels ranging from 0.03 to 0.30 wt pct Fe + Si and two dispersoid types were
investigated. Each alloy was given two heat treatments: the standard T651 heat treatment or a special thermomechanical treatment
(TMT). Fracture toughness was measured using notched round tensile specimens taken from both the longitudinal and long-transverse
directions. The notched round tensile test was modified to give the “plastic energy per unit area”. This fracture toughness
parameter gave the same ranking for corresponding alloy/heat treatment combinations as the total energy per unit area measured
on precracked Charpy specimens. The fracture toughness ranking for the ten alloys was the same in the longitudinal and long-transverse
directions. This suggests the elongated distribution of constituent particles in the rolling direction does not change the
failure mechanism. Fractographic evidence showed a bimodal distribution of ductile dimple size in all ten alloys. The number
of large ductile dimples decreased with increasing purity level while the number of small ductile dimples increased. This
is interpreted to mean that the smaller dispersoid and hardening particles become increasingly important in controlling the
fracture toughness as the large intermetallic particles are eliminated by increasing the purity of these aluminum alloys.
Since thermomechanical processing controls the amount and type of these smaller particles, it is a useful means for increasing
fracture toughness in high purity aluminum alloys. 相似文献
7.
The fatigue and fracture resistance of a TiAl alloy, Ti-47Al-2Nb-2Cr, with 0.2 at. pct boron addition was studied by performing
tensile, fracture toughness, and fatigue crack growth tests. The material was heat treated to exhibit a fine-grained, fully
lamellar microstructure with approximately 150-μm grain size and 1-μm lamellae spacing. Conventional tensile tests were conducted as a function of temperature to define the brittle-to-ductile
transition temperature (BDTT), while fracture and fatigue tests were performed at 25 °C and 815 °C. Fracture toughness tests
were performed inside a scanning electron microscope (SEM) equipped with a high-temperature loading stage, as well as using
ASTM standard techniques. Fatigue crack growth of large and small cracks was studied in air using conventional methods and
by testing inside the SEM. Fatigue and fracture mechanisms in the fine-grained, fully lamellar microstructure were identified
and correlated with the corresponding properties. The results showed that the lamellar TiAl alloy exhibited moderate fracture
toughness and fatigue crack growth resistance, despite low tensile ductility. The sources of ductility, fracture toughness,
and fatigue resistance were identified and related to pertinent microstructural variables. 相似文献
8.
Peravudh Lowhaphandu John J. Lewandowski 《Metallurgical and Materials Transactions A》1999,30(2):325-334
The effects of Cu infiltration on the monotonic fracture resistance and fatigue crack growth behavior of a powder metallurgy
(P/M) processed, porous plain carbon steel were examined after systematically changing the matrix strength via heat treatment. After austenitization and quenching, three tempering temperatures were chosen (177 °C, 428 °C, and 704 °C)
to vary the strength level and steel microstructure. The reductions in strength which occurred after tempering at the highest
temperature were accompanied by the coarsening of carbides in the tempered martensitic steel matrix, as confirmed by optical
microscopy and by microhardness measurements of the steel. Each steel-Cu composite, containing approximately 10 vol pct infiltrated
Cu, had superior fracture toughness and fatigue properties compared to the porous matrix material given the same heat treatment.
Although the heat treatments given did not significantly change the fatigue behavior of the porous steel specimens, the fatigue
curves (da/dN vs ΔK) and fracture properties were distinctly different for the steel-Cu composites given the same three heat treatments. The
fracture toughness (K
IC
and J
IC
), tearing modulus, and ΔK
TH
values for the composites were highest after tempering at 704 °C and lowest after tempering at 177 °C. In addition, the fracture
morphology of both the fracture and fatigue specimens was affected by changes in strength level, toughness, and ΔK. These fractographic features in fatigue and overload are rationalized by comparing the size of the plastic zone to the microstructural
scale in the composite.
This article is based on a presentation made in the symposium “Fatigue and Creep of Composite Materials” presented at the
TMS Fall Meeting in Indianapolis, Indiana, September 14–18, 1997, under the auspices of the TMS/ASM Composite Materials Committee. 相似文献
9.
J. Wadsworth C. M. Packer P. M. Chewey W. C. Coons 《Metallurgical and Materials Transactions A》1984,15(9):1741-1752
The mechanical properties of commercial bars of Mo and a Mo alloy have been investigated. Although longitudinal mechanical
properties are good, completely brittle behavior is invariably observed in samples tested in the transverse direction. The
microstructures of these materials have been examined using optical metallography of bar stock, scanning electron microscopy
of fracture surfaces, and Auger electron spectroscopy ofin situ fractured samples. A number of deleterious microstructural features has been identified; these include a large grain size
in the transverse direction as a result of a 〈110〉 fiber texture and fractured carbide-crack stringers on grain boundaries.
Oxygen segregation to grain boundaries has been shown not to be a factor contributing to brittle behavior. The origin of the
carbides and the development of the associated cracks are described. A thermomechanical processing route, based on a recrystallization
and forging procedure, has been developed to manufacture disc-shapes from which components having greatly improved mechanical
properties can be produced. 相似文献
10.
Ferritic Fe-Ni steels that are intended for service at low temperature are usually given an intercritical temper as the final
step in their heat treatment. The temper dramatically decreases the ductile-brittle transition temperature, TB. Its metallurgical effect is to temper the lath martensite matrix and precipitate a distribution of fine austenite particles
along the lath boundaries. Prior research suggests that the low value of TB is a consequence of the small effective grain size of the ferrite-austenite composite. The present research was done to test
this suggestion against the counter-hypothesis that the low TB is due to the inherent toughness of the constituent phases. The approximate compositions of the tempered martensite and precipitated
austenite phases in the composite microstructure of tempered 5.5Ni steel are known from STEM analysis. Bulk alloys were cast
with these two compositions. Their mechanical properties were measured after heat treatment and compared to those of the parent
alloy in the toughened ‘QLT’ condition. Both of the constituent phases are brittle at low temperature. It follows that the
outstanding low-temperature toughness of the tempered alloy cannot be attributed to the inherent properties of the constituent
phases, but must reflect their cooperative behavior in the composite microstructure. The austenitic bulk alloy was also used
to investigate the stability of the precipitated austenite phase. The thermomechanical stability of the bulk alloy approximates
that of the precipitated austenite within tempered 5.5Ni steel. This result is consistent with previous data, and supports
the conclusion that the stability of the precipitated austenite is determined mainly by its chemical composition. 相似文献
11.
Arvind Agarwal R. Balasubramaniam S. Bhargava 《Metallurgical and Materials Transactions A》1996,27(10):2985-2993
The room-temperature hydrogen embrittlement (HE) problem in iron aluminides has restricted their use as high-temperature structural
materials. The role of thermomechanical treatments (TMT),i.e., rolling at 500 °C, 800 °C, and 1000 °C, and post-TMT heat treatments,i.e., recrystallization at 750 °C and ordering at 500 °C, in affecting the room-temperature mechanical properties of Fe-25A1 intermetallic
alloy has been studied from a processing-structure-properties correlation viewpoint. It was found that when this alloy is
rolled at higher temperature, it exhibits a higher fracture strength. This has been attributed to fine subgrain size (28/μ) due to dynamic recrystallization occurring at the higher rolling temperature of 1000 °C. However, when this alloy is rolled
at 1000 °C and then recrystallized, it shows the highest ductility but poor fracture strength. This behavior has been ascribed
to the partially recrystallized microstructure, which prevents hydrogen ingress through grain boundaries and minimizes hydrogen
embrittlement. When the alloy is rolled at 1000 °C and then ordered at 500 °C for 100 hours, it shows the highest fracture
strength, due to its finer grain size. The alloy rolled at 500 °C and then ordered undergoes grain growth. Hence, it exhibits
a lower fracture strength of 360 MPa. Fracture morphologies of the alloy were found to be typical of brittle fracture,i.e., cleavage-type fracture in all the cases. 相似文献
12.
John E. Flinn Jung Chan Bae Thomas F. Kelly Gary E. Korth 《Metallurgical and Materials Transactions A》1992,23(9):2557-2565
Tensile properties and their relationship with microstructural features were investigated for a rapid solidification processed
(RSP) type 304 stainless steel (SS) extruded powder material and compared with those of a conventionally processed type 304
SS. Significant improvements in tensile strength were observed up to 800 °C (maximum test temperature) for the RSP alloy.
Stable and fine microstructural features, including grain size, small matrix precipitates, high residual dislocation density,
and a high population of nanosized void/cavities, were observed in the RSP specimens after heat treatments to0.9T
m
. The microstructural features directly re- sponsible for strengthening the RSP alloy were small grain size and the residual
dislocation density.
Formerly with
Formerly with 相似文献
13.
E. Pagounis V. K. Lindroos M. Talvitie 《Metallurgical and Materials Transactions A》1996,27(12):4183-4191
The influence of the matrix structure on the mechanical properties of a hot isostatic pressed (hipped) white iron matrix composite
containing 10 vol pct TiC is investigated. The matrix structure was systematically varied by heat treating at different austenitizing
temperatures. Various subsequent treatments were also employed. It was found that an austenitizing treatment at higher temperatures
increases the hardness, wear resistance, and impact toughness of the composite. Although after every different heat treatment
procedure the matrix structure of the composite was predominantly martensitic, with very low contents of retained austenite,
some other microstructural features affected the mechanical properties to a great extent. Abrasion resistance and hardness
increased with the austenitizing temperature because of the higher carbon content in martensite in the structure of the composite.
Optimum impact energy values were obtained with structures containing a low amount of M (M7C3+M23C6) carbides in combination with a decreased carbon content martensite. Structure austenitized at higher temperatures showed
the best tempering response. A refrigerating treatment was proven beneficial after austenitizing the composite at the lower
temperature. The greatest portion in the increased martensitic transformation in comparison to the unreinforced alloy, which
was observed particularly after austenitizing the composite at higher temperatures,[1] was confirmed to be mechanically induced. The tempering cycle might have caused some additional chemically induced transformation.
The newly examined iron-based composite was found to have higher wear resistance than the most abrasion-resistant ferroalloy
material (white cast iron). 相似文献
14.
Shen-Chih Lee Cheng-Hsun Hsu Hui-Ping Feng Chao-Chia Chang 《Metallurgical and Materials Transactions A》1998,29(10):2511-2521
Casting size affects the solidification cooling rate and microstructure of casting materials. Graphite nodules existing in
the structure of ductile iron are an inherent and inert second phase that cannot be modified in subsequent heat-treatment
processing. The matrix and the fineness of the second phase undoubtedly have some impact on the fracture toughness of the
as-cast material, as does the subsequent heat treatment, as it alters the microstructure. This research applied austempering
heat treatment to ductile iron of different section sizes and graphite nodule finenesses. The influence of these variables
on the plane strain fracture toughness (K
IC
) of the castings so treated was compared to that of the as-cast state. Metallography, scanning electron microscopy (SEM),
and X-ray diffraction analysis were performed to correlate the properties attained to the microstructural observation. 相似文献
15.
P. Ramkumar V. Anil Kumar R. K. Gupta M. K. Karthikeyan S. Narahari Prasad F. Gino Prakash K. V. A. Chakravarthi Y. Maruthi Prasad P. V. Venkitakrishnan 《Transactions of the Indian Institute of Metals》2018,71(6):1475-1485
0.3%C–CrMoV steel were processed through electric arc furnace melting followed by electro slag refining. 2800 mm diameter class of rolled rings and 8 mm thick plates required for fabrication of solid rocket booster motorcase were realized. Tensile and fracture toughness properties were evaluated as a part of characterization of the steel. Low fracture toughness in initial melts was investigated using optical and scanning electron microscopy. Modifications in methods of alloying additions/processing were suggested and incorporated to achieve the desired mechanical properties in industrial scale melts. Process was also fine-tuned by incorporating additional thermomechanical working and heat treatment cycles to achieve the required mechanical properties. Hardening cycle of 925 °C for 1 h followed by oil quenching and tempering cycle of 505 °C for 2 h followed by oil quenching was found to result in optimum combination of mechanical properties. Repeatability in processing and consistency in achieving the mechanical properties of the steel at industrial scale was demonstrated by processing 24 melts of 6 tons each into large size rings and plates. 相似文献
16.
The fracture toughness of alloy 600 and its weld, EN82H, was characterized in 54 °C to 338 °C air and hydrogenated water.
Elastic-plastic J
IC
testing was performed due to the inherent high toughness of these materials. Alloy 600 exhibited excellent fracture toughness
under all test conditions. While EN82H welds displayed excellent toughness in air and high-temperature water, a dramatic toughness
degradation occurred in water at temperatures below 149 °C. Comparison of the cracking response in low-temperature water with
that for hydrogen-precharged specimens tested in air demonstrated that the loss in toughness is due to a hydrogen-induced
intergranular cracking mechanism. At loading rates above ∼1000 MPa
, the toughness in low-temperature water is improved because there is insufficient time for hydrogen to embrittle grain boundaries.
Electron fractographic examinations were performed to correlate macroscopic properties with key microstructural features and
operative fracture mechanisms. 相似文献
17.
The effect of intermediate thermomechanical treatments on the fatigue properties of a 7050 aluminum alloy 总被引:2,自引:0,他引:2
A study was undertaken to determine the effect of microstructures produced by different ingot processing techniques on the
fatigue properties of a 7050 aluminum alloy. The different microstructures investigated were produced by hot-rolling to simulate
commercial processing (CP) methods or intermediate thermomechanical treatments (ITMT). Characterization of the microstructures
revealed that the CP 7050 material was partially recrystallized (<50 pct) due to the use of hot-rolling as the final deformation
step. The ITMT materials were examined in the as-recrystallized (AR) condition or in AR + hot rolled condition (AR + HR).
Results of the investigation showed thattotal fatigue life, both low and high cycle, were not greatly affected by the grain structures of the experimental materials. However,
metallographic studies indicated that crack initiation is probably more difficult in the fine-grained AR material. The results
of fatigue crack growth tests showed that higher crack growth rates observed at low ΔK values for ITMT {dy7050} were most likely due to the detrimental effects of undissolved Al2CuMg particles. These particles, which also contribute to low fracture toughness and higher crack growth rates at high ΔK levels, are formed during a furnace-cooling step in the ITMT processing schedule. 相似文献
18.
WC-(Fe, Ni, C) cemented carbides can be successfully transformation-toughened by careful control of binder composition and
taking into consideration the effect of thermal residual stress on the transformation characteristics of the binder. An additional
degree of control on the metastability of the binder phase can be achievedvia thermomechanical treatments. These treatments consist of transforming an austenitic binder to martensite by cooling in liquid
nitrogen followed by a suitable high temperature heat treatment to reaustenitize it. Thein situ deformation of the binder caused by the large shape and volume changes that accompany its transformation to martensite thus
provides the mechanical component of the thermomechanical treatment. Subsequent heat treatments not only reaustenitize the
binder but also modify its susceptibility to undergo stress-induced transformation. It is shown that the hardness/fracture
toughness behavior of WC-(Fe, Ni, C) cemented carbides can be significantly improved by the application of such treatments.
A qualitative explanation for the enhancements in fracture toughness provided by thermomechanical treatments is offered based
on a careful examination of the changes in phase constitution of the binder that occur during these treatments.
Formerly Manager, Research-Development, Reed Tool Company, Houston, TX. 相似文献
19.
D. Eylon J. A. Hall C. M. Pierce D. L. Ruckle 《Metallurgical and Materials Transactions A》1976,7(11):1817-1826
To establish correlations between microstructure and mechanical properties for the Ti-ll alloy, twelve different combinations
of hot die forging and heat treatment, in the a + 8 and Β phase regions, were investigated. The resulting heat treated forgings
were classified into four distinct categories based on their microstructural appearance. The room temperature tensile, post-creep
tensile, fracture toughness and fatigue crack propagation properties were measured along with creep and low cycle fatigue
at 566‡C. The creep, tensile, fatigue crack propagation and fracture toughness properties, grouped in a manner similar to
the microstructural categories. The fracture appearance and behavior of the cracks during propagation in fatigue and in fracture
toughness tests were examined, and correlations with the microstructure discussed. In the case of the fully transformed acicular
microstructure, it was found that the size and the orientation of colonies of similarly aligned α needles are dominant factors
in the crack behavior.
Formerly a National Research Council Associate, Air Force Materials Laboratory
Formerly with AFML 相似文献
20.
D. Eylon J. A. Hall C. M. Pierce D. L. Ruckle 《Metallurgical and Materials Transactions A》1976,7(12):1817-1826
To establish correlations between microstructure and mechanical properties for the Till alloy, twelve different combinations
of hot die forging and heat treatment, in the α+β and β phase regions, were investigated. The resulting heat treated forgings
were classified into four distinct categories based on their microstructural appearance. The room temperature tensile, post-creep
tensile, fracture toughness and fatigue crack propagation properties were measured along with creep and low cycle fatigue
at 566°C. The creep, tensile, fatigue crack propagation and fracture toughness properties, grouped in a manner similar to
the microstructural categories. The fracture appearance and behavior of the cracks during propagation in fatigue and in fracture
toughness tests were examined, and correlations with the microstructure discussed. In the case of the fully transformed acicular
microstructure, it was found that the size and the orientation of colonies of similarly aligned α needles are dominant factors
in the crack behavior. 相似文献