Phase transformation and age-hardening of hexagonal α′ martensite in Ti–12mass%V–2mass%Al alloys studied by transmission electron microscopy

ABSTRACTPowders of Al alloy 7091 have been consolidated by means of dynamic compaction. The dependence of density and hardness on projectile velocity has been determined. The resulting as-compacted material has been characterized using analytical transmission electron microscopy and evidence of interparticle melting observed. The microstructural responseof the compacted material to heat treatment at 523 and 723°K has been investigated.

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Microstructure and Properties of Cu-Cr-Zr-Ag Alloy

Materials Science Forum ◽

10.4028/www.scientific.net/msf.941.1613 ◽

2018 ◽

Vol 941 ◽

pp. 1613-1617 ◽

Cited By ~ 2

Author(s):

Li Jun Peng ◽

Xu Jun Mi ◽

Hao Feng Xie ◽

Yang Yu ◽

Guo Jie Huang ◽

...

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Tensile Strength ◽

Phase Transformation ◽

High Resolution ◽

Aging Process ◽

Precipitation Sequence ◽

Transmission Microscopy ◽

Transmission Electron ◽

The Matrix

The Cr precipitation sequence in Cu-Cr-Zr-Ag alloy during the aging process at 450°C could be obtained by Transmission electron microscopy (TEM) and High-resolution transmission microscopy (HRTEM) in the study. The strengthening curve shows a unimodal type and the tensile strength trends to peak when the aged for 4h. The Cr phase transformation of Cu-Cr-Zr-Ag aged at 450°C is supersaturated solid sloution→G.P zones→fcc Cr phase→order fcc Cr phase→bcc Cr phase. The orientation relationship between bcc Cr precipitates and the matrix change from cube-on-cube to NW-OR.

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Thickening of T1 Precipitates during Aging of a High Purity Al–4Cu–1Li–0.25Mn Alloy

Materials ◽

10.3390/ma12010030 ◽

2018 ◽

Vol 12 (1) ◽

pp. 30 ◽

Cited By ~ 1

Author(s):

Ines Häusler ◽

Reza Kamachali ◽

Walid Hetaba ◽

Birgit Skrotzki

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

High Purity ◽

External Load ◽

Volume Fraction ◽

Single Layer ◽

Age Hardening ◽

Defect Type ◽

Transmission Electron

The age hardening response of a high-purity Al–4Cu–1Li–0.25Mn alloy (wt. %) during isothermal aging without and with an applied external load was investigated. Plate shaped nanometer size T1 (Al2CuLi) and θ′ (Al2Cu) hardening phases were formed. The precipitates were analyzed with respect to the development of their structure, size, number density, volume fraction and associated transformation strains by conducting transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) studies in combination with geometrical phase analysis (GPA). Special attention was paid to the thickening of T1 phase. Two elementary types of single-layer T1 precipitate, one with a Li-rich (Type 1) and another with an Al-rich (Defect Type 1) central layer, were identified. The results show that the Defect Type 1 structure can act as a precursor for the Type 1 structure. The thickening of T1 precipitates occurs by alternative stacking of these two elementary structures. The thickening mechanism was analyzed based on the magnitude of strain associated with the precipitation transformation normal to its habit plane. Long-term aging and aging under load resulted in thicker and structurally defected T1 precipitates. Several types of defected precipitates were characterized and discussed. For θ′ precipitates, a ledge mechanism of thickening was observed. Compared to the normal aging, an external load applied to the peak aged state leads to small variations in the average sizes and volume fractions of the precipitates.

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In situ Transmission Electron Microscopy and Nanoindentation Studies of Phase Transformation and Pseudoelasticity of Shape-memory Titanium-nickel Films

Journal of Materials Research ◽

10.1557/jmr.2005.0226 ◽

2005 ◽

Vol 20 (7) ◽

pp. 1808-1813 ◽

Cited By ~ 22

Author(s):

X.-G. Ma ◽

K. Komvopoulos

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Phase Transformation ◽

Shape Memory ◽

Heating And Cooling ◽

Transmission Electron ◽

Different Temperatures ◽

Titanium Nickel ◽

In Situ Heating

Transmission electron microscopy (TEM) and nanoindentation, both with in situ heating capability, and electrical resistivity measurements were used to investigate phase transformation phenomena and thermomechanical behavior of shape-memory titanium-nickel (TiNi) films. The mechanisms responsible for phase transformation in the nearly equiatomic TiNi films were revealed by heating and cooling the samples inside the TEM vacuum chamber. Insight into the deformation behavior of the TiNi films was obtained from the nanoindentation response at different temperatures. A transition from elastic-plastic to pseudoelastic deformation of the martensitic TiNi films was encountered during indentation and heating. In contrast to the traditional belief, the martensitic TiNi films exhibited a pseudoelastic behavior during nanoindentation within a specific temperature range. This unexpected behavior is interpreted in terms of the evolution of martensitic variants and changes in the mobility of the twinned structures in the martensitic TiNi films, observed with the TEM during in situ heating.

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Ageing of C-Containing and C-Free Ti-15Cr and Ti-15-3

Materials Science Forum ◽

10.4028/www.scientific.net/msf.539-543.3595 ◽

2007 ◽

Vol 539-543 ◽

pp. 3595-3600

Author(s):

Xin Hua Wu ◽

Joaquin Del Prado ◽

D. Hu ◽

A. Huang ◽

M.Q. Chu ◽

...

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Grain Boundary ◽

Age Hardening ◽

Coarse Grain ◽

Analytical Transmission Electron Microscopy ◽

Hardness Testing ◽

Optical Scanning ◽

Transmission Electron ◽

Boundary Alpha

Samples of Ti-15Cr and Ti-15V-3Sn-3Al-3Cr (wt%) containing controlled additions of carbon up to 0.2wt% and different oxygen contents have been quenched and aged at temperatures between 400 and 600°C. Optical, scanning and analytical transmission electron microscopy have been used to characterise the microstructures of the quenched and aged samples. Hardness testing has been used to follow the kinetics and extent of age hardening, which are accelerated in Ccontaining samples. The addition of carbon results in the formation of Ti(CxOy) precipitates which pin grain boundaries in forged samples so that the grain size in the quenched C-containing samples is about a factor of ten less than that in the C-free samples. In the C-free samples coarse grain boundary alpha tends to form, but in the C-containing samples alpha precipitation is more uniform throughout the beta grains. The extent of omega precipitation is very different in the two alloys; the Ti-15Cr alloy forms athermal omega in the as-quenched samples and large omega precipitates are formed on ageing at 400°C. No evidence for omega has been obtained in the Ti-15-3. The hardening responses and microstructural observations are interpreted in terms of the different grain boundary oxygen contents in the C-containing and C-free samples and the different roles of omega and of carbon in the two alloys.

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