Lead is often used as regenerator material in cryocoolers because of its larger specific heat capacity in 20-30 K . However, Lead is potentially damaging to the environment and is prohibited in any device by RoHs . Therefore, it is necessary to find alternative regenerator materials [1] . Bismuth is a promising alternative material, but its specific heat is less than lead [2] . In the other hand, Er 3 Ni compound has much larger specific heat capacity relative to lead below 20K [3] . However, it is too brittle to be a proper durable regenerator material used in cryocoolers . Meanwhile, Er metal is ductile, and its the specific heat is larger than that of lead from 20 to 80K but decline rapidly below this temperature [4] . Thus we add Er into the Er 3 Ni compound as the second phase to obtain an regenerator material with excellent mechanical properties and large specific heat capacity . Er 3+x Ni alloys (x=0, 1 .436, 3 .351, 7 .819) were synthesized by arc melting Er and Ni . Heat capacities and magnetic properties were measured in physical properties measurement system (PPMS) of Quantum Design Company . The compressive strength tests were conducted according to the standard ASTM E9-09 . The compress direction is paralleled to the orientation of columnar grains . Fig .1(a) shows that the specific heat capacities of both Er 10 .819 Ni and Er 4 .436 Ni alloys are higher than lead from a very low temperature to 40K . Fig .1(b) makes a comparison between specific heat capacity curves measured and calculated by linear sum weighing volumetric proportion . Meanwhile, the magnetization versus temperature data of Er 4 .436 Ni measured in a magnetic field of 100 Oe under zero field cooled warming (ZFCW), field cooled cooling (FCC), and field cooled warming (FCW) conditions are also shown in Fig . 1(b) . The specific heat capacity curve measured shows a peak at about 7K, which is due to antiferromagnetic transition of Er 3 Ni phase in Er 4 .436 Ni alloy . However, comparing to calculation, no obvious peak at 22K is found on the curve measured . The peak at 22K on the curve calculated is from magnetic transition of Er phase . But also there is an uptrend above 25K on the curve measured relative to that calculated . The deviations maybe the magnetic transition of Er at ~22k is influenced by the second phrase Er 3 Ni in the Er 3+x Ni alloys . Fig .2 shows XRD patterns, microstructures, stress-strain curves and fractographies of Er 3+x Ni alloys (x=0, 1 .436, 7 .819) alloys . The XRD pattern and microstructures show the alloy is a combination of Er 3 Ni and Er merely . According to stress-strain curves, the compressive strength of Er 10 .819 Ni, Er 6 .351 Ni, Er 4 .436 Ni and Er 3 Ni alloys are 610 .4, 547 .6, 462 .0, 58 .0Mpa,respectively . There is a convert from brittle fracture to ductile fracture along with the increase of the addition amount of Er . When amount of Er is sufficient, Er phrase becomes the primary phrase, yet it is wrapped by net relatively harder and more brittle Er 3 Ni phrase . This makes Er 10 .819 Ni not...