Browsing by Author "Ma, CY"

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Effects of TMT on reinforcement characteristics of combustion-assisted in-situ titanium matrix composite
(1997)
Tsang, HT
;
Chao, CG
;
Ma, CY
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The effects of thermomechanical processing (TMP) on the reinforcement characteristics and mechanical properties at ambient temperature of an in-situ 10 vol.% TiC/Ti MMC produced by combustion synthesis were studied in this work. With increasingly imposed TMP, the morphology, size and distribution TiC reinforcement can be changed, refined and successfully controlled. According to the image analysis results, a linear relationship between interparticle distance and reduction of TMP can be established. Due to the refinement of TiC and the decrease of interparticle distance during TMP, both the strength and elongation are clearly enhanced. From a linear plot of strength against inverse interparticle distance, the Orowan mechanism is mainly responsible for the strengthening in this system.
Effects of volume fraction of reinforcement on tensile and creep properties of in-situ TiB/Ti MMC
(1997-11-01)
Tsang, HT
;
Chao, CG
;
Ma, CY
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Effects of volume fraction of reinforcement on tensile and creep properties of in-situ TiB/Ti MMC
(1997-11-01)
Tsang, HT
;
Chao, CG
;
Ma, CY
;
交大名義發表
;
材料科學與工程學系
Flavor-changing neutral Higgs boson couplings and top-quark-charm-quark production at the Next Linear Collider
(1997-12-01)
Hou, WS
;
Lin, GL
;
Ma, CY
;
電子物理學系
;
物理研究所
We explore the possibility of detecting flavor-changing neutral Higgs boson couplings at the Next Linear Collider (NLC) through e(+)e(-)->nu(e)<(nu)over bar>(e)t (c) over bar. In the framework of a general two-Higgs-doublet model, we perform a complete calculation and find that sigma(e(+)e(-)-->nu(e) nu(e)t (c) over bar nu(e)<(nu)over bar>(e) (t) over bar c) could reach similar to 9 fb for root s=2 TeV. This amounts to an annual production of 500 t (c) over bar plus (t) over bar c pairs at the NLC with an integrated luminosity of 50 fb(-1). The dependence of the tc-production rate on the neutral scalar mixing angle is mild except when sin(2) alpha-->0 or 1. The nu nu W+W- background should be manageable after b tagging, while vvt (t) over bar background should not be a problem when the signal event rate is still interesting. The process, together with e(+)e(-)-->nu(e)<(nu(e))over bar>W+W-,nu(e)<(nu(e))over bar>ZZ studies, offer the chance of measuring the t-c-Higgs-bsson coupling.
Flavor-changing neutral Higgs boson couplings and top-quark-charm-quark production at the Next Linear Collider
(1997-12-01)
Hou, WS
;
Lin, GL
;
Ma, CY
;
電子物理學系
;
物理研究所
We explore the possibility of detecting flavor-changing neutral Higgs boson couplings at the Next Linear Collider (NLC) through e(+)e(-)->nu(e)<(nu)over bar>(e)t (c) over bar. In the framework of a general two-Higgs-doublet model, we perform a complete calculation and find that sigma(e(+)e(-)-->nu(e) nu(e)t (c) over bar nu(e)<(nu)over bar>(e) (t) over bar c) could reach similar to 9 fb for root s=2 TeV. This amounts to an annual production of 500 t (c) over bar plus (t) over bar c pairs at the NLC with an integrated luminosity of 50 fb(-1). The dependence of the tc-production rate on the neutral scalar mixing angle is mild except when sin(2) alpha-->0 or 1. The nu nu W+W- background should be manageable after b tagging, while vvt (t) over bar background should not be a problem when the signal event rate is still interesting. The process, together with e(+)e(-)-->nu(e)<(nu(e))over bar>W+W-,nu(e)<(nu(e))over bar>ZZ studies, offer the chance of measuring the t-c-Higgs-bsson coupling.
In situ fracture observation of a TiC/Ti MMC produced by combustion synthesis
(1996-10-15)
Tsang, HT
;
Chao, CG
;
Ma, CY
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Probing flavor changing neutral Higgs couplings at LHC
(1997-09-18)
Hou, WS
;
Lin, GL
;
Ma, CY
;
Yuan, CP
;
電子物理學系
Uniquely heavy with mass at the weak scale, the top quark may have large flavor changing couplings to Higgs bosons that are as yet unexplored. We show that such couplings could be directly probed at the LHC through the parton subprocess c((c) over bar)g --> t((t) over bar)A(0), where the pseudoscalar A(0) subsequently decays into t (c) over bar or (t) over bar c, giving rise to the intriguing final state of like sign top quark pairs. After demanding l(+/-)l(+/-), missing energy and two b-jets, the major background turns out to be q (q) over bar' --> Wt (t) over bar, which can be partially suppressed by jet counting. The signal can then manifest itself in the asymmetry of numbers of l(+)l(+) and l(-)l(-) events. To further improve the signal over background, efficient t vs. (t) over bar tagging methods should be developed. (C) 1997 Elsevier Science B.V.
Probing flavor changing neutral Higgs couplings at LHC
(1997-09-18)
Hou, WS
;
Lin, GL
;
Ma, CY
;
Yuan, CP
;
電子物理學系
Uniquely heavy with mass at the weak scale, the top quark may have large flavor changing couplings to Higgs bosons that are as yet unexplored. We show that such couplings could be directly probed at the LHC through the parton subprocess c((c) over bar)g --> t((t) over bar)A(0), where the pseudoscalar A(0) subsequently decays into t (c) over bar or (t) over bar c, giving rise to the intriguing final state of like sign top quark pairs. After demanding l(+/-)l(+/-), missing energy and two b-jets, the major background turns out to be q (q) over bar' --> Wt (t) over bar, which can be partially suppressed by jet counting. The signal can then manifest itself in the asymmetry of numbers of l(+)l(+) and l(-)l(-) events. To further improve the signal over background, efficient t vs. (t) over bar tagging methods should be developed. (C) 1997 Elsevier Science B.V.
The effects of Mg microaddition on the mechanical behavior and fracture mechanism of MAR-M247 superalloy at elevated temperatures
(1999-03-01)
Bor, HY
;
Chao, CG
;
Ma, CY
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The effects of microadditions of Mg on the mechanical behavior and fracture mechanism of MAR-M247 superalloy were investigated in this study. The microstructural observations and image analysis showed that a Mg microaddition ranging from 30 to 80 ppm significantly changed the primary MC carbide characteristics and inhibited the scriptlike carbide formation. After a 80 ppm Mg addition, the elongation measured at 1172 K increased over 3 times found that for the Mg-free MAR-M247 superalloy. The creep life and rupture elongation of the MAR-M247 superalloy with 80 ppm Mg was also improved up to 3 to 5 times that of the alloy without Mg during a 1033 K/724 MPa creep test. The fracture analyses demonstrated that cracks were mainly initiated and propagated at the interface of scriptlike MC carbides in the Mg-free MAR-M247 superalloy at elevated temperatures. The Mg microaddition effectively refined and spheroidized these coarse carbides so that a change in the crack initiation occurred from the carbide/matrix interface to that along the gamma-gamma' eutectic. Interfacial analysis using Auger electron spectroscopy illustrated that Mg segregated to the interface of the MC carbide/matrix, causing a change in the morphology and interfacial behavior of the carbides. This improvement contributed to a prolonged rupture life and upgraded the moderate temperature ductility of the MAR-M247 superalloy.
The influence of magnesium on carbide characteristics and creep behavior of the Mar-M247 superalloy
(1997-12-22)
Bor, HY
;
Chao, CG
;
Ma, CY
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The influence of Mg on creep properties and fracture behaviors of Mar-M247 superalloy under 1255 K/200 MPa
(2000-05-01)
Bor, HY
;
Chao, CC
;
Ma, CY
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The effects of Mg microadditions on the high-temperature/low stress (1255 K/200 MPa) creep properties and fracture behavior of a Mar-M247 superalloy were investigated in this study. The results of quantitative statistical analyses showed that when Mg microadditions up to 50 ppm were made, the MC carbides located at grain boundaries (designated GB MC) were significantly refined and spheroidized and the number of MC carbides decreased. In addition, the M23C6 carbides present on GBs dramatically increased with increasing Mg contents up to 50 ppm, and the creep resistance was enhanced under the test condition of 1255 K/200 MPa. However, the creep performance of a Mar-M247 superalloy containing 80 ppm Mg deteriorated due to the formation of an extremely large amount of MC carbide and a decrease in the number of M23C6 carbides at GBs. The cracks mainly initiated and propagated along GBs in both the Mg-free and Mg-containing Mar-M247 superalloys under 1255 K/200 MPa, and the finial rupture was caused by intergranular fracture. Under the present creep condition, the optimal Mg microaddition to a Mar-M247 superalloy should be 30 to 50 ppm.