Progress in Earth andPlanetary Science

Ohtani et al.
Progress in Earth and Planetary Science(2022) 9:24
https://doi.org/10.1186/s40645-022-00482-7

Open Access

RESEARCH ARTICLE

Experimental simulations of shock texturesin BCC iron: implications for iron meteorites
Eiji Ohtani1* , Toru Sakurabayashi1 and Kosuke Kurosawa2

Abstract
Neumann band in iron meteorites, which is deformation twins in kamacite (Fe–Ni alloy), has been known to be acharacteristic texture indicating ancient collisions on parent bodies of meteorites. We conducted a series of shock
recovery experiments on bcc iron with the projectile velocity at 1.5 km/s at various initial temperatures, room temperature, 670 K, and 1100 K, and conducted an annealing experiment on the shocked iron. We also conducted numericalsimulations with the iSALE-2D code to investigate peak pressure and temperature distributions in the nontransparent
targets. The effects of pressure and temperature on the formation and disappearance of the twins (Neumann band)
were explored based on laboratory and numerical experiments. The twin was formed in the run products of theexperiments conducted at room temperature and 670 K, whereas it was not observed in the run product formed by
the impact at 1100 K. The present experiments combined with the numerical simulations revealed that the twin wasformed by impacts with various shock pressures from 1.5–2 GPa to around 13 GPa. The twin in iron almost disappeared by annealing at 1070 K. The iron meteorites with Neumann bands were shocked at this pressure range andtemperatures at least up to 670 K, and were not heated to the temperatures above 1070 K after the Neumann bandformation.
Keywords: Neumann band, Twin, Impact, Iron meteorite, Shock experiment, iSALE-2D code
1 Introduction
Wasson (1967) and Wasson et al. (1998) analyzed 700
iron meteorites, initially for Ni, Ga, Ge, and Ir and later
for Cr, Co, Cu, As, Sb, W, Re, Pt, and Au, using instrumental neutron activation analyses. Based on these analyses, iron meteorites have been divided into 13 groups
according to their chemical compositions (Goldstein
et al. 2009). The Neumann band has been observed in
kamacite (body-centered cubic [bcc] phase) separated as
the Widmanstätten pattern in most groups of iron meteorites such as Goose Lake IAB (Scott 2020) and IVA,
IVB, and ungrouped iron meteorites such as Hammondand Babb’s Mill (Blake’s Iron and Troost’s Iron) (Yanget al. 2011).

*Correspondence: eohtani@tohoku.ac.jp
1
Department of Earth Science, Graduate School of Science, Tohoku
University, Sendai 980‑8578, Japan
Full list of author information is available at the end of the article

Both carbonaceous chondritic (CC)-type and noncarbonaceous (NC)-type iron meteorites fractionatedin their parent bodies in the early stage of formation of
the solar system, perhaps within 1–3 My after the formation of calciumaluminum-rich inclusions in the solar
nebula (Kruijer et al. 2017; Hilton et al. 2019; Scott 2020).
Such early metal–silicate fractionation occurred perhaps
because of melting caused by the radiogenic heating byextinct radiogenic elements such as 26Al (e.g., Goldstein
et al. 2009). Therefore, iron meteorites possess information on their early differentiated planetesimals.
Many iron meteorites, however, have experienced textural deformation because of mutual collisions, which
would modify the original information. Therefore, if we
accurately understand the impact conditions requiredfor producing the shock features in iron meteorites, wewould be able to decode the impact environment in theearly solar system.

© The Author(s) 2022. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which
permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to theoriginal author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images orother third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line
to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory
regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of thislicence, visit http://​creat​iveco​mmons.​org/​licen​ses/​by/4.​0/.

Ohtani et al. Progress in Earth and Planetary Science(2022) 9:24

Although magnitudes of the shock events in ordinarychondrites have been classified as the shock stage from
S1 to S6 based on their shock textures (Stöffler et al.
1991), there are few systematic classifications of shockstages in iron meteorites. Yang et al. (2011) made aneffort to classify the four shock stages for IVA, IVB, andsome ungrouped iron meteorites based on various shocktextures. According to them, the Neumann band is aprominent signature of stage 1, which shows the recordsof relatively weak collisions, and it can be removed byannealing caused by the later heating events. Therefore,
the formation and disappearing conditions of the Neumann band are useful to identify unaltered or less-alterediron meteorites after their formation in the early solar
system. Because of such importance, we made experimental simulations of the formation and disappearanceof the Neumann band.
The Neumann band has been known to be a deformation twin (Uhlig 1955) formed by the intracrystalline plastic deformation in many metals. This deformation twin in
bcc iron shows the twin boundary of (112) and moving
directions of atoms along [111] on the twin boundaries(Calister and Rethwisch 2000; Murr et al. 2002a). It has
been considered that the Neumann band in iron meteorites was formed by mutual collisions between planetesimals (Bischoff and Stöffler 1992).
Murr et al. (2002a, b) conducted impact experimentswith bcc iron and SUS304 (an austenitic stainless steel),and observed deformation twins in the recovered ironsamples. Their shock experiments reported velocities
at 0.5–3.8 km/s and measured the depths where twins
formed. Based on the relations of the impact velocity
and the depths of the twin formation, they estimatedthat an impact velocity greater than 0.1 km/s (equivalent to 1 GPa) is needed for producing twins (Murr et al.
2002b). Although impact experiments on iron–nickel
alloys at low temperatures down to 110 K (Marchi et al.
2020) and those of iron at 76–573 K (Rohde 1969) havebeen conducted previously, these experiments did not
make detailed analyses pertaining to twin formation anddisappearance.
In this study, we conducted laboratory and numericalexperiments with bcc iron targets at a variety of initial
temperatures to investigate the structural changes of ironagainst a propagation of compressive pulse. We reproduced deformation twins experimentally in bcc iron andrevealed the temperature and pressure dependence of thetwin formation. We also conducted an annealing experiment on iron having twins to explore the temperature
required for their disappearance. We discussed the formation and disappearance conditions of Neumann bands
in shocked iron meteorites based on our experiments andnumerical simulations.

Page 2 of 15

2 Experimental methods
We conducted shock recovery experiments with a lightgas gun. An iron projectile was accelerated onto an irontarget. We observed the shock textures including deformation twins in the recovered samples. Here, we summarize the shock apparatus, heating system to realize thehigh-temperature impact experiments, and procedure ofanalyses of the samples recovered from the impact experiments. We also conducted numerical simulations to estimate the pressure and temperature distributions in irontargets under the same impact conditions archived in thelaboratory experiment.
2.1 Two‑stage light gas gun used for the impact
experiments

The two-stage light gas gun installed in the Institute of
Fluid Science of Tohoku University, Japan, was used toaccelerate a projectile. The instrument is schematicallyshown in Fig. 1. Helium gas was compressed by a piston
made of high-density polyethylene (33 mm in diameterand 60 mm in length). A mylar film (500 µm in thickness)
was used as the second diaphragm to confine the gaspressure. The pistons before and after the experiment are
shown in Additional file 1: Figure S1. We generated the
projectile velocity of 1.5 km/s in the present experiments.
The detailed information on the two-stage light gas gun
is given elsewhere (e.g., Shinohara 2002). We employed
the laser light blocking method to measure the projectile velocity, V, and the impedance matching method to
calculate the pressure at the epicenter (Miller et al. 1991;
Ahrens 1987). The projectile velocity was determinedfrom the time of the flight between two laser beams with
the interval of 520 mm. We employed a GaAs semiconductor laser with a power of 3.2 mW (Kikoh Giken Co.,

Fig. 1 The two-stage light gas gun (installed at Institute of Fluid
Science, Tohoku University) used for impact experiments to simulate
the formation of a Neumann band. A schematic image of the
instrument components is also shownOhtani et al. Progress in Earth and Planetary Science(2022) 9:24

Page 3 of 15

Ltd., Hyogo, Japan). The error in velocity estimation
was 1% or less. We present each experimental condition
including the impact velocity in Table 1.
2.2 Projectile and target material

The projectile and target samples were iron with thepurity of 99.9%. The projectile used in the present experiment is shown in Additional file 2: Figure S2 and Table 1.
The projectile body was made of polycarbonate with
10 mm in diameter and 13.5 mm in length. A bcc irondisk with 8 mm in diameter and 3.5 mm in height wasplaced at the top of the polycarbonate body. The total
weight of the projectile was 2.5 g.
Bcc iron was also used as the target. The samples wereshaped into cylinders with a diameter of 38 mm and aheight of 20 mm or 30 mm. The longer target was usedin the experiments at high temperatures (670 K and1100 K). The iron sample was placed in a molybdenum
capsule (50 mm in outer diameter, 38 mm in inner diameter, depth of 8 mm, and height of 10 mm) to heat theiron sample effectively using the induction furnace. The
target iron sample embedded in a molybdenum capsule isshown in Additional file 3: Figure S3.
2.3 Heating and the temperature measurementof the sample

We heated the target samples before the impact of the
projectile to investigate the effect of initial temperatureon the textures of the shocked samples. We used an
induction furnace (TRD-02001, Dai-ichi Kiden Co. Ltd.,Tokyo, Japan) for heating the target samples. A schematic
image of the sample chamber with the induction furnaceand the temperature measurement system is shown in
Fig. 2. The induction coil of the furnace was covered by aceramic brick cylinder with an outer diameter of 70 mm
and an inner diameter of 50 mm (as shown in Fig. 2) toavoid damaging the coil from the fragments of the projectile and target during impact. The target iron sample
and induction furnace were placed in the sample chamber of the two-stage light gas gun. The sample chamber

Fig. 2 A schematic image of the sample chamber with the heating
and temperature measuring systems used for the two-stage light gas
gun

was evacuated using a rotary vacuum pump to 20 Pa,
which is within the suitable condition of heating by the
induction furnace (667 Pa). The temperature of the sample surface was measured by radiation from the sample using an optical pyrometer (IR-CAS2TN, CHINO
Co. Ltd., Tokyo, Japan). We measured the irradiance at
0.9 µm using the silicon detector for temperature measurement. The uncertainty of the sample temperature
measurement was ± 5 °C below 1000 °C. The image of theheated sample and the temperature reading of the opticalpyrometer on the sample surface at the time of collisionwere recorded by a video camera (DM-FVM30, Canon,
Co. Ltd, Tokyo, Japan). The heating rate was about 7 K/
min, and the cooling rate by shutting off the electricalsupply was 20 K/min. The two-stage gas gun was operated within one minute after shutting off the electricalsupply for heating for safety. Thus, the uncertainty of theexperimental temperature was within 20 K. The sample temperature is assumed to be homogeneous and thesame as that on the surface because of heating by the
induction furnace and high thermal conductivity of bcc

Table 1 Conditions for the impact and annealing experiments
Second diaphragm

PistonRun 011

Mylar, 0.5 mm

HDPE

Run 012Mylar, 0.5 mm

HDPE

Run 013Mylar, 0.5 mm

HDPE

Run 011H*––

Projectile

TargetMaterial

Weight (g)Velocity (km/s)

Material

Size (D × H), mm

PC + iron

38 × 20

PC + iron

2.46

1.53

Iron

PC + iron

2.43

1.51

Iron

2.43

1.47

Iron

–

–

–

Iron

HDPE, High-Density Polyethylene: PC, Polycarbonate*annealing experiment, **Height × Width × Thickness

Temperature, K
300

38 × 30

1100

18 × 2 × 1**

1070

38 × 30

670

Ohtani et al. Progress in Earth and Planetary Science(2022) 9:24

iron, which is shown in the literature to range from 23­mm2s/ at 300 K to 5 ­mm2/s at 1000 K (Monaghan andQuested 2001).
2.4 Analysis of the recovered samples

Figure 3 shows the backscattered electron (BSE) image(a) and secondary electron image (SEI) (b) of the textureof the etched bcc iron target material. The grain size ofPage 4 of 15

the starting material was 100–200 µm in diameter. Craters were formed in the iron targets after the impact
experiments as shown in Fig. 4. To observe the shocked
texture of the recovered sample, we cut the sample into
two pieces and polished it with silicon carbide and finediamond powders making a mirror surface of the crosssection across the center of the crater. We etched thepolished surface with Nital for a few seconds to perform

Fig. 3 The backscattered electron (BSE) image (a) and secondary electron image (SEI) (b) of the etched iron starting material

Fig. 4 The images of craters formed by impacts at room temperature (Run 011), (a), 1100 K (Run 012), (b), and 670 K (Run 013) (c), and theirpolished cross sections

Ohtani et al. Progress in Earth and Planetary Science(2022) 9:24

Page 5 of 15

textural observation of the polished cross section. The
textual observations were conducted using a reflective
optical microscope (Nikon PTIPHOT2-POL) and a scanning electron microscope (JEOL JSM5410).
We determined the number of twins in the rectangle region with the size of 400 μm × 300 μm at different
depths of the polished samples measured from the crater
surface of the target. We also measured the mean grain
sizes of the samples and obtained the number density oftwins in individual grain (number per unit area, 1/cm2) asshown in Table 2. We did not measure the grain orientations in the recovered samples in this measurement.

of the shocked iron, we employed the constitutive equations in the simulations. We used the Johnson–Cookstrength model (JNCK) with the parameters pertaining
to ARMCO-iron (Johnson and Cook 1983) because therelation between stress and strain for ARMCO-iron has
been well understood (e.g., Johnson and Cook 1983) andthe ARMCO-iron contains a small fraction of impurities,
which is less than 1%. The JNCK parameters and calculation settings used in the calculations are listed in Tables 3
and 4, respectively.

2.5 Shock physics modeling using iSALE‑2D code

We conducted three shock experiments at room temperature (Run 011), 1100 K (Run 012), and 670 K (Run013). The projectile collided with the sample at a velocityof 1.53(± 0.02) km/s at room temperature (Run 011). Figure 4a shows the crater and its polished cross section. The
crater with a diameter of 17.8 mm and a depth of 6.8 mm
was formed by the impact under this condition. Figure 5
shows the BSE images of the texture of the polished section and the SEI of the highly magnified textures of different depths near the crater. A composite BSE image of thewhole sample is shown in Fig. 6. In the region from thesurface down to 1.0-mm depth, we observed concentric
flow textures of grains as shown in Fig. 5. We observed

We conducted two-dimensional impact simulations using
the iSALE shock physics code (Amsden et al. 1980; Ivanov
et al. 1997; Wünnemann et al. 2006) to estimate the pressure and temperature distributions in the nontransparent
samples during the laboratory experiments. We used thetwo-dimensional version of the iSALE, which is referred
to as iSALE-Dellen (Collins et al. 2016). A cylindricalcoordinate was employed to model vertical impacts performed in the experiments. The analytical equations ofstate (ANEOS) (Thompson and Lauson 1972) pertaining to iron (Thompson 1990) were used for both the ironprojectile and target. To treat the elastoplastic behavior

3 Results
3.1 The deformation twins created by the impact

Table 2 Number Density ­(cm−2) of Neumann bands with depths for the collision at room temperature (Run 011), 670 K (Run 013), andafter annealing at 1070 K for 10 min (Run 011H)
Depths (mm)Number in 400 µm ×
300 µmMean grain size(µm)

Std dev. (µm)

Number density in one
grain ­(cm−2)

Pressure (GPa)*

3.0 (1.2) × 1­ 05

12.7

2.2 (1.1) × 1­ 05

7.65

Run 011 Collision at 300 K
2.9

361

134

26

6

384

125

30

7.7

269

102

24

9

314

129

33

11.6

131

115

38

13.8

87

113

37

4.9

421

154

25

6.4

297

157

34

9.3

382

206

25

15.4

184

200

21

20

11

170

42

Run 013. Collision at 670 K

Run 011H. Annealing at 1070 K for 10 min
2.7

40

68

15

7

65

128

37

9.2

55

137

35

11.8

53

143

50

16.4

45

126

40

*Pressure was estimated by impact simulation (see text)

3.2 (1.5) × 1­ 05

9.26

2.6 (1.3) × 1­ 05

6.71

5

5.41

7.3 (4.7) × 1­ 04

4.07

3.5 (1.1) × 1­ 05

10.2

3.2 (0.8) × 1­ 05

7

1.1 (0.7) × 1­ 0

2.5 (1.1) × 1­ 05

8.8

1.5 (0.3) × 1­ 05

3.89

9.2 (4.5) × 1­ 03

2.45

3.3 (1.5) × 1­ 04–

4.6 (2.3) × 1­ 04–

3.8 (2.4) × 1­ 04–

5.4 (3.1) × 1­ 04–

4.4 (3.1) × 1­ 04–

Ohtani et al. Progress in Earth and Planetary Science(2022) 9:24

Page 6 of 15

Table 3 Models and parameters used for simulation with theiSALE 2D code

Table 4 Calculation settings used in the numerical simulations
with the iSALE*

Parameters used for simulation

ARMCO iron (Johnson and Cook
1985)

Computational geometry

Analytical EOS (ANEOS)

Thompson (1990)

R direction

330

Melting temperature

1811

Z direction

600

Specific heat (J/kg K)

452

Strength model

Johnson–Cook (JNCK) model

JNCK parameters

Cylindrical coordinate

Number of computational cells

Number of cells per projectile radius
Radial direction

57

Vertical direction

25

A(MPa)

175

B(MPa)

380

Radial direction

271

N

0.32

Vertical direction

214 (670 K, 1100 K) 143 (300 K)

C

0.06

0.24

M

0.55

Artificial viscosity ­a1

1.2

Tref(K)

298

Artificial viscosity ­a2
Impact velocity (km ­s-1)

The same archived in theexperiments

linear textures with 20 µm length and 0.5 µm width in
this region. In the region from 1.0- to 2.6-mm depths, weobserved twins together with flow textures. In the deeper
region from 2.6 mm to 15.5 mm, we only observed twins(see Figs. 5 and 6). The number of twins decreases withdepth in this sample.

Number of cells per target radius

High-speed cutoff

2-fold impact velocity

Low-density cutoff (kg ­m-3)

100*Detailed descriptions of the parameters can be found in the iSALE manual(Collins et al. 2016)

Fig. 5 The optical and backscattered electron (BSE) images of the texture of the polished section adjacent to the crater surface within 3-mm
depths of the sample impacted at room temperature (Run 011). Its high magnification secondary electron images (SEI) are also shownOhtani et al. Progress in Earth and Planetary Science(2022) 9:24

Fig. 6 The optical and backscattered electron (BSE) images fromthe top to the bottom of the target sample of the room temperature
impact (Run 011) and its magnified secondary electron images (SEI).
The twins are observed in the images

In the experiment conducted at 1100 K (Run 012), we
used a 30-mm-long sample to investigate the temperature effect on the twin formation. The temperature of thesample was increased to 1110 K first, then we turned off
the electric power of the induction furnace, and the projectile was accelerated to a velocity of 1.51(± 0.02) km/s.
Because the cooling rate of the sample was slow (20 K/
min as mentioned), the sample temperature at the timeof the collision was estimated to be 1090–1110 K in thisexperiment. Figure 4b shows the polished section of therecovered sample. A 22.4-mm-wide and 10.1-mm-deep
crater was formed by the impact at 1100 ± 10 K. Figure 7
shows the BSE image of the texture of the whole sample. The polished textures of this sample (Run 012) wereremarkably different from those of the shocked sample atPage 7 of 15

room temperature (Run 011). We did not find any flow
textures but observed polygonal crystals with a grain sizeof about 70 µm from beneath the crater down to a depthof 2.6 mm. We also observed polygonal crystals with alarger grain size of 100–200 µm in the deeper regions,and we did not identify any twins to the rear surface ofthe sample.
In the third experiment (Run 013), the projectile
was collided with a 30-mm-long sample at the velocity of 1.47(± 0.02) km/s at 670 K. The recovered sample and its cross section are shown in Fig. 4(c). The
diameter and the depth of the crater were 16.2 mm
and 6.5 mm, respectively. The BSE images of the wholeviews of the polished section, and magnified local SEI
images are shown in Fig. 8. Grains with several tens µm
in diameter were observed in the sample at the depths
of 1.2 mm. Both the flow textures and twins wereobserved at depths from 1.2 to 2.5 mm. We observed
only twins at depths from 2.5 mm to around 20 mmof the sample, as shown in Fig. 8. The number of twins
decreased with the depths of the sample. The craters
have slightly asymmetrical shapes, as shown in Fig. 4.
Although the cause of asymmetry is not well known,
it could be because of a slightly tilted collision of the
projectile.
We conducted an annealing experiment on theshocked target at room temperature, which has thedeformation twins. The recovered sample from Run 011
was shaped into a plate with the size of 18 mm height× 2 mm width × 1 mm thickness. The plate was heated
for ten minutes at 1070 K, which is below the bcc–fcc
phase boundary (1123 K) and was cooled to room temperature with a cooling rate of 20 K/min. The BSE and
SEI images of the whole view of the plate after annealing at 1070 K (Run 011H) are shown in Fig. 9. Although
we observed the oxidized layer with a thickness around
50 µm on the surface of the annealed sample, we did
not observe the oxidized layer in the deeper interior of
the heated sample. We observed remarkable changes intextures after annealing at 1070 K for ten minutes. The
flow patterns formed near the crater by the room temperature impact (Run 011) disappeared to form polygonal grains with a size of 40–100 µm (Run 011H).
3.2 Impact simulation using iSALE‑2D code

We conducted the impact simulations under the same
conditions, including the sample temperatures, using
iSALE-2D code. The distributions of the peak pressure
and temperature during the impacts at room temperature, 1070 K, and 670 K are shown in Fig. 10. The depth
profiles of the peak pressure and temperature along

Ohtani et al. Progress in Earth and Planetary Science(2022) 9:24

Page 8 of 15

Fig. 7 The optical and backscattered electron (BSE) images of the polish section and the magnified secondary electron images (SEI) of the different
positions of the sample recovered from the impact at 1100 K (Run 012)

the central axis of the iron targets of these impacts areshown in Fig. 11. An increase in pressure to 30 GPa wasobserved within the 5-mm depths from the craters for
all the runs, whereas the pressure decreased graduallyfrom 10 GPa to less than 1 GPa at the depths greaterthan 5 mm to the bottom of the target samples. The
temperature profiles also showed similar distributions,as shown in the bottom column of the figure. A rapid
increase in temperature appeared at depths shallower
than 5 mm, whereas the temperature increase was limited below 160 K in the region deeper than 5 mm depth,

and the temperature increase was negligible from the
10 mm depth to the bottom of the target samples. The
present simulation is consistent with the shock pressureof 30 GPa estimated by the shock Hugoniot (Bischoffand Stöffler 1992; Murr et al. 2002a) at the top of thecrater within the 5-mm depths; however, the pressure
decayed continuously to below 2 GPa at the bottom of
the sample. Therefore, it is important to consider thisdecay of the maximum pressure when discussing theformation conditions of twins.

Ohtani et al. Progress in Earth and Planetary Science(2022) 9:24

Page 9 of 15

Fig. 8 The optical and backscattered electron (BSE) images of the sample impacted at 670 K (Run 013) and the secondary electron images (SEI)
magnified locally

3.3 Distribution of deformation twins in iron target
samples

Variations in the density of twins within the target samples for three experiments (Runs 011, 013, and 011H)
are summarized in Fig. 12. Because we did not observe
any twins in the shocked target at 1100 K (Run 012), thedata obtained only at room temperature and 670 K areshown. The absence of the twins in this sample is consistent with the result of the annealing experiment.
The distribution of twins was expressed as their density in a unit area (Number/cm2) in one grain of the sample following the definition of the dislocation density

in crystals and is shown in Table 2. The twin was notobserved near the crater surface to 5-mm depths perhaps because of an intensive deformation associatedwith the pressure and temperature increase to 30 GPa
and above 800 K, respectively, in the impacts at room
temperature and 670 K. No significant difference in thenumber density profiles with pressure was observed
between the samples collided at room temperature (Run011) and 670 K, as shown in Fig. 12b. The distribution oftwins annealed at 1070 K below the bcc–fcc transition for
10 min (Run 011H) shows a remarkable reduction of thenumber density at all depths, as shown in Fig. 12a.

Ohtani et al. Progress in Earth and Planetary Science(2022) 9:24

Page 10 of 15

cannot produce the twins possibly because of too highdislocation density in one grain. Therefore, the Neumann band can be used as a shock indicator between
1.5–2 GPa and around 13 GPa. The relations between
the twin density and pressure are also presented asshown in Fig. 12b. We found that the twin density canbe well fitted by a simple linear relation as a functionof peak pressure. The phase boundary between bcc andhcp iron locates at around 13 GPa. Figures 11 and 12
also suggest saturation of the twin density due to large
deformation. Although we observed the texture afterpressure release, the recent in situ XRD measurementsof the released stages from shocked iron using XFEL
(Hwang et al. 2020) suggested the process occurredin the large deformation region of our recovered samples, i.e., the phase change occurred very quickly andeven fcc phase could be formed due to expansion of thesamples. These processes likely occurred in the highly
deformed regions of our samples.
We found that the initial temperature does not largely
affect the twin density at least up to 670 K, indicating thatthe production rate of twins is high enough to neglect
the effects of annealing kinetics at least below 670 K. The
present experiments combined with the numerical simulations revealed that the Neumann band was shocked by
impacts with shock pressures from 1.5–2 GPa to around
13 GPa and temperatures at least up to 670 K.
4.2 Annealing and disappearance of twins
Fig. 9 The BSE image from the top to the bottom of the recovered
sample annealed with the induction furnace at 1070 K for 10 min, andits locally magnified SEI images (Run 011H)

4 Discussion
4.1 Conditions for twin formation combining impact
experiments and simulations

The twins were formed even near the rear surfaces of thetarget samples where the shock pressures decayed below
2 GPa estimated by the iSALE (Fig. 11a, c), suggestingthat the threshold pressure of the twin formation is close
to 1.5–2 GPa. Murr et al. (2002b) reported the relation of
the impact velocity and the depth of twin formation andestimated the threshold impact velocity for the twin formation to be 0.1 km/s (corresponding to 1 GPa) at room
temperature, which is consistent with our observations.
We can estimate the thermal history of iron meteorites experienced during and after collision based on
their shock textures. Our experiments revealed that
the Neumann band is a signature of shock above 1.5–2GPa, which can be formed by impacts below temperatures about 670 K. However, our result also showedthat too high degrees of compression above 13 GPa

Our annealing experiment (Run 011H) revealed thattwins disappeared easily in bcc iron by annealing andrecrystallization at 1070 K below the bcc–fcc transition
temperature only for ten minutes. This observation isconsistent with experimental results of high-temperatureannealing of iron meteorites conducted by Jain and Lipschutz (1968), Buchwald (1975), and Davidson (1940).
These previous annealing experiments on iron meteorites
indicated that the samples recrystallized at temperatures
above 870 K, which is below the bcc–fcc phase transition boundary, after 0.5–3 h of annealing. Annealing
experiments on heavily deformed iron, Fe–0.3 wt%Al,
and Fe–0.3 wt%Si alloys also indicated that recrystallization started at temperatures above 770 K with a heating
rate of 10 K/min and significant grain growth occurred at1070 K (Tomita et al. 2017), which is also consistent with
our observation of twin disappearance in the shocked
iron sample.
Recrystallization including reduction of dislocation
density has been studied extensively (Humphreys et al.
2017). The conventional analysis for recrystallization
may be applied to reduce the twin density by recrystallization, and the decrease rate may be expressed by anempirical n-th order recrystallization kinetics expression,Ohtani et al. Progress in Earth and Planetary Science(2022) 9:24

Page 11 of 15

Fig. 10 The results of numerical simulations on distributions of the maximum temperature (left) and pressure (right) in the iron targets during theimpacts at 300 K (a), 1100 K (b), and 670 K (c) corresponding to the experimental conditions of Run 011, 012, and 013. The color contour on the left
side indicates the peak temperature, Kelvin, and that on the right side is the peak pressure in GPadρ/dt = −kρn, where k is the rate constant for recovery(Humphreys et al. 2017), and ρ is the twin density. Different values are proposed for n-values depending on thematerials; n = 2 for the recovery of olivine (Farla et al.
2010) and LiF (Li 1962), n = 2 (Van Drunen and Saimoto 1971) or 3 (Prinz et al. 1982) for Cu, and n = 3 forNi (Prinz et al. 1982). Therefore, we adopted n = 2 and3 for decrease in twin density by annealing. By fitting
our data by this equation, dρ/dt can be obtained with aparameter k = 3.084 × ­10–8 for n = 2 and k = 4.316 × ­10–13
for n = 3 at 1070 K for 10 min. Based on this equation,
we can estimate the time dependency of the decrease in
twin density for various durations from 1 min to 1 h at
1070 K as shown in Fig. 13a. Significant reduction of thetwin density occurred by annealing at 1070 K as shown inthis figure.

Decrease in twin density because of annealing andrecrystallization at different temperatures may be estimated by the temperature dependence of the rate constant, k, which can be expressed by k = k0exp(− Ea/RT),
where Ea is the activation energy for the process considered, k0 is a constant, R is the gas constant, and T
is the temperature. Because we obtained k(1070 K), as
mentioned, we can obtain a temperature-dependent
rate constant k(T) if Ea is given. The activation energy
for the recovery is expected to be close to the self-diffusion of the metals for Cu (Cottrell and Aytekin 1950), Fe(Michalak and Paxton 1961), and Zn (Van Drunen and
Saimoto 1971). Experiments on recovery/recrystallization of steel suggest the activation energy, Ea, is around250 kJ/mol, which is close to that of the iron self-diffusion (e.g., Watanabe and Karashima 1970; Glover andStellars 1973). Therefore, the activation energy of 250
kJ/mol was adopted in the recrystallization of twins.

Ohtani et al. Progress in Earth and Planetary Science(2022) 9:24

Page 12 of 15

Fig. 11 The results of the iSALE-2D simulation on distributions of the peak pressure (GPa) and temperature (K) along the center axis of thetarget. The distribution of peak pressure (a) and temperature (b) in the room temperature impact (corresponding to Run 011), the peak pressure(c) and temperature (d) in the impact at 670 K (corresponding to Run 013), and the peak pressure (e) and temperature (f) in the 1100 K impact(corresponding to Run 012). The distance from the crater is shown as the depth in mm

Fig. 12 a The twin density from the top to the bottom of the samples recovered from the impacts at room temperature (Solid squares, Run 011)
and 670 K (Open circles, Run 013). The density after annealing at 1070 K (Open squares, Run011H) for 10 min is also shown. The twin distribution isexpressed as a linear relation, N ­(cm−2) = 4.14 × ­105–2.34 × ­104 × D (mm) (R = 0.908) for the room temperature impact, and N ­(cm−2) = 4.45 × ­105–
2.05 × ­104 × D (mm) (R = 0.936) for the impact at 670 K, where N is the density of twins in a unit area of 1 c­ m2, and D is the depth of the sample
from the crater surface in mm. (b) The relation between the twin density and pressure (GPa) that was deduced by the iSALE-2D simulation.
The relation can be expressed by N ­(cm−2) = –6.30 × ­104 + 4.11 × ­104 × P (GPa) (R = 0.905). All data for room temperature (solid squares) and
670 K (open circles) are included for the fitting except a data point (*) at 13 GPa in which the twin density close to the crater may be reduced byincreasing pressure and temperature

Ohtani et al. Progress in Earth and Planetary Science(2022) 9:24

Page 13 of 15

Fig. 13 The effect of time (a) and temperature (b) for annealing of twins assuming n = 2 and 3 for decreasing rate expressed by an empirical n-thorder recrystallization kinetics expression, dρ/dt = −kρn, where k is the rate constant for recrystallization (see the text for more details). a Decreasein twin density by annealing during time intervals from one minute to one hour at 1070 K and various depths of the sample for n = 2 (blue curves)and for n = 3 (red dotted curves). The experimental data for Run 011 and Run 011H (10-min annealing at 1070 K) are shown as black open and red
open circles, respectively. b The change in twin density by annealing at various temperatures and durations from one minute to one hour for n = 2(blue curves) and n = 3 (red curves). The initial twin density before annealing was taken as 3.5 × ­105 ­cm−2, and the activation energy Ea of 250 kJ/
mol was adopted for the recrystallization process of twins

Finally, we can estimate the temperature dependenceof the disappearance of twins, as shown in Figure 13b.
This figure indicates annealing and disappearanceof twin occur above 700 K, which is consistent withannealing experiments on iron meteorites (Jain andLipschutz 1968; Buchwald 1975). This is the reason why
the shocked sample at 670 K was free from the annealing. In our impact experiment conducted at 1100 K(Run 012), we cannot observe twins in the iron target,
as shown in Figure 7. The cooling rate after the impact
at 1100 K is estimated to be 20 K/min as shown in
Sect. 2.2. Therefore, the disappearance of twins at 1100
K impact (Run 012) annealed for 10 min during coolingto 900 K is consistent with the recrystallization rate oftwin estimated here.
Our experiments showed that twins were formed by
impacts at least up to 670 K, and it was not formed byhigh-temperature impacts above 1100 K. The annealing experiment and the analysis of the kinetics given in
Fig. 13a and b revealed that the twin in iron disappeared
easily by reheating and annealing at 1070 K.
The bcc–fcc transition temperature in iron is 1184 K,
whereas the transition of kamacite with 5–7.5 mol% Ni
occurs at 770–905 K (Reisener and Goldstein 2003).
Therefore, the maximum temperature for survival of
the Neumann band in kamacites might be as low as thetemperature of the bcc–fcc equilibrium phase boundary. Although we used iron in this study, our result may

provide insight into Neumann band formation in ironmeteorites because kamacite can survive even at 1070 K
metastably because of sluggish transition kinetics (Dunlop and Özdemir 2007) when it was reheated rapidly.
Therefore, iron meteorites with Neumann bands were
not heated to the temperatures above 1070 K after the
Neumann band formation.

5 Conclusions
A series of shock recovery experiments at three different
sample temperatures were conducted using a two-stage
light gas gun with an induction furnace. Textures of therecovered iron were studied with the impact velocity
of about 1.5 km/s in the temperature range from room
temperature to 1100 K. The twin was observed in therun products of room temperature and 670 K, whereas it
was not observed in the run product recovered from theimpact at 1100 K.
We conducted numerical simulations of these impacts
to estimate the maximum pressure and temperature
distributions in the targets during the impacts. We
revealed that the twin can be formed at relatively low
pressures from 1.5–2 GPa to around 13 GPa at low temperatures at least up to 670 K. The present experiments
combined with the numerical simulations revealed that
the Neumann band was shocked at this pressure range
by impacts and temperatures at least up to 670 K. Our
annealing experiments also implied that the twin in iron

Ohtani et al. Progress in Earth and Planetary Science(2022) 9:24

recrystallizes and disappears easily by heating at around1070 K. Iron meteorites with Neumann bands were notheated above 1070 K after the Neumann band formation.

Page 14 of 15

Author details
1
Department of Earth Science, Graduate School of Science, Tohoku University,
Sendai 980‑8578, Japan. 2 Planetary Exploration Research Center, Chiba Institute of Technology, Chiba 275‑0016, Japan.
Received: 28 July 2021 Accepted: 18 April 2022

Abbreviations
SUS304: Steel Use Stainless 304; Nital: Ethanol containing 5 vol % of nitricacid; BSE: Backscattered electron; SEI: Secondary electron image; bcc: Bodycentered cubic; iSALE: Shock physics code for impact-simplified arbitrary
Lagrangian Eulerian; JNCK: Johnson–Cook strength model; ANEOS: Analyticalequation of state developed for shock physics; ARMCO-iron: Pure iron produced by American Rolling Mill Company.

Supplementary Information
The online version contains supplementary material available at https://​doi.​
org/​10.​1186/​s40645-​022-​00482-7.
Additional file 1. Fig. S1: The piston made of high-density polyethylene(HDPE) used for the first stage of compression. A piston before the impact
experiment (a) and that after the experiment (b).
Additional file 2. Fig. S2: The projectile used for the impact experiments.
Additional file 3. Fig. S3: The target sample (iron rod) in a molybdenum
capsule.
Acknowledgements
The authors appreciate W. McDonough for stimulating discussion on this work
including the origin of iron meteorites. The authors thank Akio Suzuki of Graduate School of Science, Tohoku University, and Professor (Emeritus) Kazuyoshi
Takayama and technical staff of Institute of Fluid Science, Tohoku University
for helping them conduct shock experiments and analyze recovered samples.
The authors appreciate the developers of iSALE, including G. Collins, K.
Wünnemann, B. Ivanov, J. Melosh, and D. Elbeshausen. The authors also thank
Tom Davison for the development of the pySALEPlot. This work was supported by JSPS KAKENHI, JP11874071, JP09304051, and JP20H00187 to EO. KK
was supported by JSPS KAKENHI JP18H04464, JP19H00726, and JP21K18660.
This article is dedicated to Ahmed El Goresy who studied shocked meteorites
and made excellent contributions to meteoritics and high-pressure mineral
physics.
Author contributions
EO devised the project, designed the experiments, prepared the heating
system, and attended the impact experiment. TS prepared the samples,
conducted the impact experiments, and collected data and analyzed therecovered samples. KK conducted iSALE-2D simulation of the impacts. EO andKK wrote the manuscript with inputs from TS. All authors read and approved
the final manuscript.
Funding
This work was supported by JSPS KAKENHI, JP11874071, JP09304051,
and JP20H00187 to EO. KK was supported by JSPS KAKENHI JP18H04464,
JP19H00726, and JP21K18660.
Availability of data and materials
All data are available in the main text and the supplementary materials. Additional data may be available from the corresponding authors upon reasonable
request.

Declarations
Competing interests
The authors declare that they have no competing interest.

References
Ahrens TJ (1987) Shock-wave techniques for geophysics and planetary physics. In: Sammis CG, Henyey TL (eds) Methods of experimental physics.
Academic Press, New York, pp 185–235
Amsden A, Ruppel H, Hirt C(1980) Sale: a simplified ale computer programfor fluid flows at all speeds. Technical report LA-8095 Report, Los Alamos
National Laboratories
Bischoff A, Stöffler D (1992) Shock metamorphism as a fundamental process
in the evolution of planetary bodies: information from meteorites. Eur J
Mineral 4:707–755
Buchwald VF (1975) Secondary structure of iron meteorite, Chapter 11,
125–136, in Handbook of iron meteorites, vol. 1, University of Hawaii
Calister WD, Rethwisch DG (2000) Materials science and engineering: an introduction, 8th edn. Wiley, Hoboken
Collins GS, Elbeshausen D, Davison TM, Wünnemann K, Ivanov BA, Melosh
HJ (2016) iSALE-Dellen manual. Figshare. https://​doi.​org/​10.​6084/​m9.​
figsh​are.​34736​90.​v2
Cottrell AH, Aytekin VJ (1950) The flow of zinc under constant stress. InstMet 77:389
Davidson AB (1940), The effect of annealing on Neumann bands. Electronictheses and dissertations. Paper 1705. https://​doi.​org/​10.​18297/​etd/​
1705
Dunlop DJ, Özdemir Ö (2007) Iron and iron-nickel, treatise on geophysics.
Treatise Geophys 5:277–336
Farla RJM, Kokkonen H, Fitz Gerald JD, Barnhoorn A, Faul UH, Jackson I(2010) Dislocation recovery in fine-grained polycrystalline olivine. Phys
Chem Miner. https://​doi.​org/​10.​1007/​s00269-​010-​0410-3
Glover G, Stellars M (1973) Recovery and recrystallization during high temperature deformation of α-Iron. Metall Trans 4:765–775
Goldstein JI, Scott ERD, Chabot NL (2009) Iron meteorites: Crystallization,
thermal history, parent bodies, and origin. Chem Erde Geochem
69:293–325
Hilton CD, Bermingham KR, Walker RJ, Timothy J, McCoy TJ (2019) Genetics,
crystallization sequence, and age of the South Byron Trio iron meteorites: new insights to carbonaceous chondrite (CC) type parent bodies.
Geochim Cosmochim Acta 25:217–228
Humphreys J, Rohrer GS, Rollett A (2017) Recrystallization and related
annealing phenomena, 3rd edn. Elsevier, Netherlands, 691p.
ISBN978-0-08-098235-9
Hwang H, Galtier E, Cynn H, Eom I, Chun SH, Bang Y, Hwang G, Choi J, Kim T,
Kong M, Kwon S, Kang K, Lee HJ, Park C, Lee JI, Lee Yongmoon, Yang W,
Shim S-H, Vogt T, Kim Sangsoo, Park J, Kim Sunam, Nam D, Lee JH, Hyun
H, Kim M, Koo T-Y, Kao C-C, Sekine T, Lee Y (2020) Subnanosecond phasetransition dynamics in laser-shocked iron. Sci Adv 6:eaaz5132
Ivanov BA, Deniem D, Neukum G (1997) Implementation of dynamic strength
models into 2-D hydrocodes: applications for atmospheric breakup andimpact cratering. Int J Impact Eng 20:411–430
Jain AV, Lipschutz ME (1968) Implications of shock effects in iron meteorites.
Nature 220:140–143
Kruijer TS, Burkhardt C, Budde G, Kleine T (2017) Age of Jupiter inferred fromthe distinct genetics and formation times of meteorites. Proc Natl Acad
Sci 114(2017):6712–6716
Li JCM (1962) Possibility of subgrain rotation during recrystallization. J Appl
Phys 33:2958–2965
Marchi S, Durda DD, Polanskey CA, Asphaug E, Bottke WF, Elkins‐Tanton LT,
et al (2020) Hypervelocity impact experiments in iron‐nickel ingots andiron meteorites: Implications for the NASA Psyche mission. J Geophys Res
Planets 125:e2019JE005927. https://​doi.​org/​10.​1029/​2019J​E0059​27

Ohtani et al. Progress in Earth and Planetary Science(2022) 9:24

Michalak JT, Paxton HW (1961) Some recovery characteristics of zone melted
iron. Trans AIME 221:850–857
Miller GM, Stolper EM, Ahrens TJ (1991) The equation of state of molten
komatiite 1. Shock wave compression to 36 GPa. J Geophys Res
96(B7):11831–11848
Monaghan BJ, Quested PN (2001) Thermal diffusivity of iron at high temperature in both the liquid and solid states. ISIJ Int 41:1524–1528
Murr LE, Trillo EA, Bujanda AA, Martinez NE (2002a) Comparison of residual
microstructures associated with impact craters in fcc stainless steel
and bcc iron target: the microtwin versus microband issue. Acta Mater
50:121–131
Murr LE, Bujanda AA, Trillo EA, Martinez NE (2002b) Deformation twins associated with impact craters in polycrystalline iron target. J Mater Sci Lett
21:559–563
Prinz F, Argon AS, Moffatt WC (1982) Recovery of dislocation structures in plastically deformed copper and nickel single crystals. Acta Metall 30:821–830
Reisener RJ, Goldstein JI (2003) Ordinary Chondrite metallography: part 1.
Fe-Ni taenite cooking experiments. Meteorit Planet Sci 38:1669–1678
Rohde RW (1969) Dynamic yield behavior of shock-loaded iron from 76 to
573°K. Acta Metall 17:353–363
Scott ERD (2020) Iron meteorites: composition, age, and origin. Oxf Res Encycl
Planet Sci. https://​doi.​org/​10.​1093/​acref​ore/​97801​90647​926.​013.​206
Shinohara M (2002) Study of development of a compact two-stage light gas
gun and its ignition system. Master of Science thesis, Institute of Fluid
Science, Tohoku University
Stöffler D, Keil K, Scott ERD (1991) Shock metamorphism of ordinary chondrites. Geochim Cosmochim Acta 55:3845–3867
Thompson SL, Lauson HS (1972) Improvements in the Chart D radiationhydrodynamic CODE III: Revised analytic equations of state. Rep. SC-RR-71
0714, pp 1–119, Sandia Natl. Lab., Albuquerque, NM
Thompson SL (1990) ANEOS analytic equations of state for shock physics
codes input manual. Sandia report, SAND89-2951·UC-404
Tomita M, Inaguma T, Sakamoto H, Ushioda K (2017) Recrystallization behavior
and texture evolution in severely coldrolled Fe-0.3mass%Si and Fe0.3mass%Al Alloys. ISIJ Int 57:921–928
Uhlig HH (1955) Contribution of metallurgy to the origin of meteorites, part
II—the significance of Neumann bands in meteorites. Geochim Cormochim Acta 7:34–42
Van Drunen G, Saimoto S (1971) Deformation and recovery of [001] oriented
copper crystals. Acta Metall 19:213–221
Wasson JT (1967) The chemical classification of iron meteorites. I(Ge and Ga
concentration in selected Fe meteorites used to determine quantizationin terms of multiple parent body hypothesis and planetary fractionation
processes). Geochim Cosmochim Acta 31:161–180
Wasson JT, Choi B-G, Jerde EA, Ulff-Møller F (1998) Chemical classification ofiron meteorites: XII. New members of the magmatic groups. Geochim
Cosmochim Acta 62:715–724
Watanabe T, Karashima S (1970) An analysis of high temperature creep
in alpha iron based on the super jog mechanism. Trans Jpn Inst Met
11:159–165
Wünnemann K, Collins G, Melosh H (2006) A strain-based porosity model foruse in hydrocode simulations of impacts and implications for transient
crater growth in porous targets. Icarus 180:514–527
Yang J, Goldstein I, Scott ERD, Michael JR, Kotula PG, Pham T, McCoy TJ (2011)
Thermal and impact histories of reheated group IVA, IVB, and ungroupediron meteorites and their parent asteroids. Meteorit Planet Sci 46:1227–
1252. https://​doi.​org/​10.​1111/j.​1945-​5100.​2011.​01210.x

Publisher’s NoteSpringer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Page 15 of 15